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SpaceX to push the envelope on 3rd Starship test flight (space.com)

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[–]yash13[S] 219 points220 points  (45 children)

Among the bold goals are "opening and closing Starship's payload door, a propellant transfer demonstration during the upper stage's coast phase, the first ever re-light of a Raptor engine while in space and a controlled reentry of Starship," SpaceX wrote in a mission description.

[–]JJ82DMC 155 points156 points  (8 children)

Opening the payload door is easy when your rocket explodes. Just saying.

[–]diederich 83 points84 points  (0 children)

Closing afterwards is tricky.

[–]loungesinger 14 points15 points  (6 children)

Explosion? No. Rapid Unscheduled Disassembly? Yes.

[–]Luhnkhead 6 points7 points  (1 child)

More like Energetic Payload Expulsion

[–]DaoFerret 3 points4 points  (0 children)

Unscheduled Cargo Disembarkment

[–]Ishana92 3 points4 points  (1 child)

Rapid sort-of-scheduled payload door opening

[–]wwants 31 points32 points  (31 children)

How exactly is the propellant transfer supposed to work on a single ship? What propellant is transfered from where to where?

Edit: other commenters are saying “Lox header tank to the main lox tank.” I’m still trying to figure out what purpose this serves.

[–]descisionsdecisions 108 points109 points  (17 children)

Pumping liquid in zero g is difficult since it can just float around in the tank rather than being forced by gravity. I bet they are just making sure it works since it is so critical to all their future plans for starship.

[–]Objective_Economy281 28 points29 points  (1 child)

I bet they are just making sure it works since it is so critical to all their future plans for starship.

That, and there’s also a NASA cash prize or something like that for the first group to demonstrate doing it (at a certain volume, which probably only spaceX can do).

[–]mfb- 22 points23 points  (0 children)

https://www.nasa.gov/technology/2020-nasa-tipping-point-selections/

SpaceX of Hawthorne, California, $53.2 million

Large-scale flight demonstration to transfer 10 metric tons of cryogenic propellant, specifically liquid oxygen, between tanks on a Starship vehicle. SpaceX will collaborate with Glenn and Marshall.

[–]wwants 21 points22 points  (14 children)

Thank makes sense. Thank you for sharing

[–]ergzay 45 points46 points  (13 children)

To further clarify in addition to the above post (which is still completely correct), they're also doing the test because it's specifically one of the milestones in the NASA HLS contract. The milestones are the checkpoints at which SpaceX receives payments for milestones completed (contrary to popular belief, SpaceX did not get a lump sum of their entire contract value from the moment it was awarded).

Also pumping cryogenic fluids within a vehicle isn't that different than pumping cryogenic fluids between vehicles. The hard part of moving fluids is the actual moving of the fluids, not the establishing of a connection.

[–]Capt_Pickhard 7 points8 points  (8 children)

How do they move fluids around in zero G reservoirs? Do the tanks rotate or something? Or have inner spinning corkscrew type walls?

[–]ergzay 21 points22 points  (6 children)

SpaceX hasn't said what their plan is specifically (as far as I'm aware). The fan community has guessed that the two most likely options are a rotation to settle the fluids and then pump them or a gradual acceleration (possibly via venting tank pressure) to effectively "drain" one tank into the other.

[–]notfromchicago 4 points5 points  (3 children)

Could they possibly use injection instead of pumping? Have a diaphragm in the tank and push the fluids into the other tank. Possibly use the vacuum of space to fill the other side of the diaphragm and push the plunger so to say.

I'm high AF laying in bed about to go to sleep. Just laying here talking out my ass. But I think they could possibly find a way to transfer it that doesn't involve pumping.

[–]quickstatcheck 10 points11 points  (0 children)

A diaphragm would be pretty easy for room temp water, but it would be a material science challenge to do it with highly reactive substances at cryogenic temperatures.

[–]Martianspirit 9 points10 points  (0 children)

That's what they do for hypergolic propellant transfers from Progress to the ISS. The propellant is in elastic bladders. But there is no suitable material that works with cryogenic propellant. Besides it would have quite a large mass penalty.

Ullage thrust is what is used to settle propellant for upper stage relight. It is the most straightforward method for cryogenic propellants.

IMO the biggest challenge is establishing the connection between 2 ships. At the pad they use the quick disconnect arms but it is still tricky, They keep optimizing them. They gain experience there that they can utilize for connecting ships in space.

[–]ergzay 1 point2 points  (0 children)

Have a diaphragm in the tank and push the fluids into the other tank.

Do you have an idea for a material that acts flexible under cryogenic temperatures? Most rubbers for example turn into easily shattered glass at those temperatures.

SpaceX I doubt wants to go that deep into R&D.

[–]BEAT_LA 0 points1 point  (1 child)

Yes they have. Differential pressure between target and source.

[–]ergzay 2 points3 points  (0 children)

That doesn't answer the question. Differential pressure doesn't move fluids unless the fluids are actually in the location you need them to be in. Otherwise the gasses will just equalize without moving any fluid.

[–]Brusion 7 points8 points  (0 children)

FYI, Apollo and lots of other programs use ullage thrusters. Small rocket motors that provide some acceleration to settle the fluid in the tank at the "bottom".

[–]kog 2 points3 points  (3 children)

The milestone for Starship HLS is ship-to-ship propellant transfer. This will probably help them achieve that sooner, but they still have a ways to go to do it for credit.

[–]Shrike99 5 points6 points  (2 children)

The milestone for Starship HLS is ship-to-ship propellant transfer.

Yes, how however SpaceX do have a separate contract with NASA for internal propellant transfer demonstration on a Starship vehicle, so while not strictly an HLS milestone as /u/ergzay stated, they will still be getting paid for this.

One could also argue that NASA may have awarded this contract with the intention of supporting HLS technology development, in which case it wouldn't be too much of a stretch to consider it an HLS milestone.

[–]ergzay 1 point2 points  (0 children)

Ah true, mixed up the HLS milestones and the additional propellant transfer demo non-milestone contract. It's a minor difference though.

[–]kog -1 points0 points  (0 children)

It doesn't really matter compared to the real milestone. NASA won't do CDR for Starship HLS until SpaceX demonstrate ship-to-ship propellant transfer.

[–]ndnkng 14 points15 points  (0 children)

To prove they have a pump system that works in zero g to transfer cryo fuel.

[–]Berkee_From_Turkey 8 points9 points  (7 children)

Purpose of adjusting the rockets centre of mass, probably to stablaize it. Of its too high or low it'll want to flip, if it's centered it'll be more stable. Check out some KSP :)

[–]wwants 1 point2 points  (6 children)

Very cool. Is there a reason why the propellant ends up in the header tank instead of the main tank when the ship reaches orbit?

[–]New_Poet_338 6 points7 points  (1 child)

When the ship is landing, it freefalls until it relights its engines just before reaching the ground. The main tank is largely drained on the way to orbit, with just enough for a several second burn to deorbit and land, so the fuel in there is sloshing around the tank and can't be used to feed the engines when this landing relight begins. The header has a few seconds of fuel under pressure to start the engines in free fall, so the remaining fuel in the main tanks can settle for that several second landing burn.

[–]Martianspirit 3 points4 points  (0 children)

The whole flop and landing burn is done from the header tanks.

[–]Berkee_From_Turkey 2 points3 points  (3 children)

I'm assuming theres 2 tanks and they're simply moving contents from one to the other. Probably uses some propellant to keep stable and minor adjustments while in flight? Idk how exactly the starship works, maybe they'll just use some up while in vacuum and they wanna balance out before reentry

[–]wwants 3 points4 points  (1 child)

Yeah I’m hoping we get some details on this during the live broadcast. I’m actually touring the factory in Hawthorne today so I’ll see if anyone knows anything about it.

[–]Accomplished-Crab932 4 points5 points  (0 children)

The vehicle has the primary tanks located at the base of the ship. Additionally, there are a pair of spherical tanks in the nose that remain full throughout operation.

They have to be full for landing as the main tanks will be empty and/or partially full, which is not acceptable for the flip maneuver needed. However, their placement is entirely due to mass distribution on the ship for descent, where without them, the center of mass would be very close to the engine bay, which is bad for control of the ship during descent.

[–]Bensemus 1 point2 points  (0 children)

The header tanks make the ship more stable when reentering and they hold the fuel needed for the landing burn. The small tanks are full so the fuel can’t slosh around and expose the pickups, resulting in gas bubbles in the engines which often causes them to blow up.

[–]7473GiveMeAccount 1 point2 points  (1 child)

To validate their simulations on eg cryo fluid behavior in the real world, which alone makes this worth doing, and also to test out systems like valves, flow meters (not at all trivial), their system for very tightly controlling differential pressure between the tanks, etc

large scale cryo fluid transfer in orbit is far from easy, and starting on a somewhat smaller scale within a single vehicle is a sensible path

[–]wwants 0 points1 point  (0 children)

Thank you for sharing. That’s very interesting.

[–]LongJohnSelenium 2 points3 points  (0 children)

Pumping liquid is straightforward. You just need a tiny bit of ullage thrust to settle the tanks. Virtually every rocket with relight capabilities demonstrates active pumping in space.

A tiny bit of thrust is needed to settle the tanks and then pumping happens fine

The really big question mark for this test is that they're transferring cryogenic liquids, and what exactly happens when you take really cold liquids and put it in relatively warm piping while in low g acceleration is not exactly known.

[–]Greenawayer 1 point2 points  (0 children)

opening and closing Starship's payload door

Just hope they have haven't named the Starship's computer "HAL".

That didn't work well the last time.

[–]UnnervingS 83 points84 points  (24 children)

If they get to orbit my expectations will have been surpassed.

[–]hms11 54 points55 points  (14 children)

I'm feeling reasonably confident Starship hits its orbital target this time.

It would have made it last time, the Raptors were flawless. It was a venting strategy that ended up being a bad idea that did it in last time.

My predictions are:

- Starship makes it to it's targeted "orbit".

- Superheavy survives the hot stage AND manages to properly do it's boost back burn, probably managing a soft landing in the ocean because the boost back burn is the trickiest bit of that setup.

- Starship payload doors open and close like planned.

- 50% chance of orbital fuel transfer functioning properly.

- 50% chance raptor in-space relight goes properly.

- 20% chance Starship survives re-entry.

​

I think hammering out the heat tiles will be the next big issue. While the stainless steel Starship is FAR more resilient than shuttle, that ship is still losing quite a few tiles on ascent every time. I'm guessing they will lose this thing on re-entry and the next major iteration will be figuring out how to either keep those tiles in place, or figure out another solution that is less susceptible to mounting failure.

[–]Accomplished-Crab932 26 points27 points  (0 children)

To be fair about the tiles, the previous vehicles just had tiles attached. They weren’t tested using a force gauge like S28’s or the shuttle’s.

I’d expect tile losses, but less than we saw on S25.

[–]ergzay 13 points14 points  (1 child)

I would say don't get too optimistic on getting to orbit. There's a whole avalanche of "unknown unknowns" that they likely still haven't hit yet. It's still very much a test program. They would've figured out more of them if they were allowed to test more rapidly.

[–]mfb- 11 points12 points  (0 children)

I see IFT-2 similar to the third Falcon 1 flight: It failed due to a procedural issue, but the rocket would have been capable of reaching orbit. The fourth flight of Falcon 1 reached orbit with no hardware changes, they only gave the first stage a bit more time to stop its residual thrust before doing stage separation.

It's possible that something unexpected makes the flight fail, but I think it's likely to reach orbit. Even the much older hardware on IFT-2 was ready for that.

[–]vilette 4 points5 points  (4 children)

you are quite pessimistic for re-entry, what will fail ?

[–]hms11 20 points21 points  (0 children)

My guess is that either it will lose stability due to an aerodynamic factor not simulated or will lose a couple heat tiles in a vulnerable and critical location.

[–]Icarus_Toast 3 points4 points  (0 children)

SpaceX is trying to use smaller heat shield tiles so they can mass produce them when the time comes. It's an untested strategy. So far on every launch and static fire that had the tiles attached, some of them have fallen off. It's unknown how critical of a vulnerability this poses. It could range from not being a problem at all to 100% chance of failure. It's also pretty well unknown whether success would hinge on luck (the correct tiles in the correct spots remaining attached).

There's just so many variables with the re-entry that we don't know about. I'm sure the smart folks at SpaceX have a much better idea than we do though. I'm excited to see it attempted.

[–]hms11 4 points5 points  (0 children)

My guess is that either it will lose stability due to an aerodynamic factor not simulated or will lose a couple heat tiles in a vulnerable and critical location.

[–]SpringrollJack -4 points-3 points  (0 children)

He’s pretty optimistic. I would say around 0% is more likely

[–]0hmyscience 1 point2 points  (0 children)

Why are you so pessimistic of the relight?

Also, I didn't see it mentioned in the article, but if the orbital fuel transfer test fails, the missing is probably still a go, correct?

[–]Fredasa 0 points1 point  (0 children)

  • 20% chance Starship survives re-entry.

Far as I understand things, they're still using glue for the tiles along the seams, which all but guarantees that most of them will dislodge. While I'm not expecting Starship to survive reentry, I do hope we get some good camera footage out of it. Live footage from Starship and recorded footage from observational flights over whatever sea Starship will be targeting.

[–]drjaychou 0 points1 point  (2 children)

Is Starship going to be re-usable like the smaller rockets? If so is it going to land like they do, or just splash and get picked up?

[–]Ishana92 6 points7 points  (0 children)

It is supposed to do the belly flop maneuvre and vertical landing. They kind of sort of did it once with just the ship.

[–]AggravatingValue5390 3 points4 points  (0 children)

The eventual plan is to belly flop through the atmosphere and flip at the last second to land like the Falcon 9 boosters, but that is not going to be attempted in this test. Here's a test of their flip and burn procedure so you can see what their goal is

[–]Fredasa 7 points8 points  (6 children)

I'm mainly wondering if they'll be able to repeat having all 33 (and all 6) engines lit. It was a complete surprise with IFT2, and there's little to suggest that the reliability of the engines has reached a point where we can expect a repeat this time. Obviously a lost engine or two won't ding the mission, but I personally consider engine reliability to be as much of a WIP as the tile situation.

[–]BrangdonJ 5 points6 points  (1 child)

It wasn't a complete surprised for IFT2. SpaceX had said the failures in IFT1 were due to using old (and mismatched) engines. IFT2 had newer, improved engines. They were expected to perform better.

[–]Fredasa -1 points0 points  (0 children)

I'm crossing my fingers. I think if they weren't still replacing engines on the current stack pretty recently, I'd have more confidence on this point.

[–]A3bilbaNEO 4 points5 points  (0 children)

Booster 10 did fire all 33 for 10 seconds, both on the first try and with no previous spin-prime test, let's hope for the best!

[–]UnnervingS 2 points3 points  (2 children)

Completely agreed. Testing campaign so far for IFT3 has been fairly short and the engines have been exposed to salt air for quite a while due to delays. I'm sure this is well accounted for but I'll be impressed if all engines fire for the first burn. I'll be amazed if all engines relight.

[–]wgp3 2 points3 points  (0 children)

But like you said, test campaign has been short. It took much longer for the 2nd flight to get off the ground so those engines would have been exposed to the elements for longer. And those were older engines as well. So these should fair better from that fact alone. Then we know that this current booster also managed to static fire all engines for the planned test duration on their first go. Before then they had never done that successfully on a static fire.

So all signs point to this part of things maturing nicely and should become less and less of a concern. There's always the chance that they have made an error in their processes and procedures though that may have overlooked something and therefore we see a regression compared to the second flights engine performance.

[–]Fredasa 0 points1 point  (0 children)

Yep. If things go more or less as planned during this mission, I expect the peanut gallery to latch onto any engine non-ignition as a "one step backward" from what we saw in IFT2. Even if they know enough not to believe it themselves, it will be an important component of their anti-SpaceX campaign.

[–]0hmyscience 3 points4 points  (0 children)

That's how I felt for ITF-2. I was hoping that at minimum we'd have successful stage separation, which is what happened.

This time I'm hoping that at a minimum they start the belly-flop maneuver with the ship, and that the booster is in one piece imminently before touching the water.

In terms of it surviving re-entry, I would've been extremely skeptical of that happening for ITF-1 or ITF-2. But to be honest I don't know how much better the heat tiles have gotten in the mean time. I remember seeing them fall off all the time but that's not something I hear about anymore, so perhaps this time they have a realistic chance.

[–]Emble12 2 points3 points  (0 children)

I don’t believe they’re going for orbit with this one, they’re aiming for the Indian.

[–]vaeryidan 107 points108 points  (10 children)

They just do things completely differently to what we were used to for decades. And thank god they did. A return to the early approach of rocket testing: lots of test launches and rapid iteration.

[–]GarunixReborn 14 points15 points  (8 children)

Imagine if the first 2 launches never happened, what kind of issues would they have missed?

[–]Objective_Economy281 24 points25 points  (4 children)

They’d have probably found them on the next launches. That’s how it works.

[–]Fredasa 2 points3 points  (0 children)

That's actually one of my favorite thought experiments, and something I love to bring up whenever people talk about IFT1's crater.

The difference between the yes-IFT1 timeline and the no-IFT1 timeline would have fundamentally been that in the latter case, they wouldn't have had IFT1's flight data. That's really it. The retrofit to Stage 0, and the FAA's subsequent approval of said, occurred in both timelines and took basically the same amount of time to finish in each.

The naysayers—the ones who arbitrarily have a chip on their shoulders for this entire program and pray that it stumbles—basically fall into two camps: the ones who legitimately believe IFT1 was an embarrassing setback, and the ones who possess enough intuition and understanding of the situation to privately acknowledge that it was the best option, even given how things turned out.

[–]gbsekrit 6 points7 points  (0 children)

I really want to see a deep dive into what their telemetry flow looks like

[–]twiddlingbits 54 points55 points  (9 children)

if it fails but they learn how to fix the issue and do better it is a success! The propellant transfer is the one I will be impressed with if it happens.

[–]red75prime 7 points8 points  (8 children)

Where to they intend to transfer propellant? From payload into the main tank? The article says nothing about it.

[–]Beaver_Sauce 28 points29 points  (7 children)

Lox header tank to the main lox tank.

[–]wwants 1 point2 points  (6 children)

Do you know why this is necessary?

[–]Beaver_Sauce 20 points21 points  (5 children)

Texhnical test for NASA's Artemis program and SpaceX's own Starship on orbit refueling.

[–]wwants 2 points3 points  (4 children)

Interesting. So is it more of a testing of capability for future applications rather than a function needed for individual starship flights?

[–]ergzay 13 points14 points  (0 children)

It's needed for the HLS program (part of the Artemis moon landings) and for Starship to deliver any significant amount of cargo beyond low earth orbit.

[–]Accomplished-Crab932 10 points11 points  (1 child)

Kind of.

For anything in LEO, ie: Starlink, no. It’s not needed.

If you want to put a 100 ton satellite to Geosynchronous, or a 100 ton probe or vehicle on an interplanetary mission, this is a must.

For the Artemis program, both Blue Origin and SpaceX require the transfer of large amounts of cryogenic propellants to operate their landers. This has never been done before, with the closest analogues being the bag-tank refueling of the ISS by progress spacecraft.

Demonstrating the capability to transfer propellant gives SpaceX more money (they were contracted to demonstrate this), and proves that the system is possible, leading to the transfer of propellant between two vehicles once Starship begins flying more regularly.

[–]wwants 3 points4 points  (0 children)

Thank you for this excellent explanation

[–]MerrySkulkofFoxes 24 points25 points  (0 children)

Good strategy. A slower iterative approach would just try to nail a solid up and back. But if there's a good chance it might blow up and it's going to get ditched anyway, pack it all on and aim for the best. Lots of stuff will fail and they'll learn a lot. If they get 70% of what they're aiming for before the ship is destroyed one way or another, cool. Move fast and break spaceships.

[–]Beahner 15 points16 points  (0 children)

I like it being pushed. Some people that don’t closely follow think Falcon just showed up and started succeeding. It took this kind of testing. Hell, the very early survival of the company happened with this approach. No way they won’t push live flight testing like this.

It’s the scope and ambition of this platform that makes it feel like it could take a few more tries to get right. Not Starship and it’s Raptor, I think this works as soon as this launch.

The hot stage and boost back will be most interesting to watch. I don’t know enough technical to know how hard that will be to solve, im sure it will, but I’m not totally sure it will be this time.

I’m not speaking from a level of expertise, but from a level of enjoying this program and feeling nervous about this maneuver.

[–]Decronym 3 points4 points  (0 children)

Acronyms, initialisms, abbreviations, contractions, and other phrases which expand to something larger, that I've seen in this thread:

Fewer Letters More Letters
CDR Critical Design Review
(As 'Cdr') Commander
FAA Federal Aviation Administration
FAR Federal Aviation Regulations
HLS Human Landing System (Artemis)
KSP Kerbal Space Program, the rocketry simulator
LEO Low Earth Orbit (180-2000km)
Law Enforcement Officer (most often mentioned during transport operations)
MECO Main Engine Cut-Off
MainEngineCutOff podcast
TVC Thrust Vector Control
Jargon Definition
Raptor Methane-fueled rocket engine under development by SpaceX
Starlink SpaceX's world-wide satellite broadband constellation
apogee Highest point in an elliptical orbit around Earth (when the orbiter is slowest)
cryogenic Very low temperature fluid; materials that would be gaseous at room temperature/pressure
(In re: rocket fuel) Often synonymous with hydrolox
hydrolox Portmanteau: liquid hydrogen fuel, liquid oxygen oxidizer
hypergolic A set of two substances that ignite when in contact
perigee Lowest point in an elliptical orbit around the Earth (when the orbiter is fastest)
ullage motor Small rocket motor that fires to push propellant to the bottom of the tank, when in zero-g

NOTE: Decronym for Reddit is no longer supported, and Decronym has moved to Lemmy; requests for support and new installations should be directed to the Contact address below.

15 acronyms in this thread; the most compressed thread commented on today has 24 acronyms.
[Thread #9824 for this sub, first seen 7th Mar 2024, 23:03] [FAQ] [Full list] [Contact] [Source code]

[–]whiteb8917 20 points21 points  (21 children)

They are always pushing the envelope.

TF1 the goal was to get it off the pad. IT DID, it got to Max-q but things went pear shaped after Max-Q before stage sep, along with engine damage from the pad.

TF2 the goal was to Hot stage. IT DID. All engines performed flawlessly, Stage Separated, but I think the flip caused the fuel to become unstable and starved the engines, it self destructed. Starship got to 150 Kilometers and JUST short of its intended velocity before it was lost.

TF3 is getting to orbit, no question........, this is after 3 flights, Falcon took more flights before it got to orbit.

[–]wgp3 3 points4 points  (0 children)

This keeps having to be said, but there was no engine damage from the pad according to SpaceX and any of the documentation they supplied the FAA from what the public can see.

The engines were just older and less reliable. More prone to leaks, lacking fire suppression, and lacking blast shielding. So when some didn't start right they leaked and the heat from the others caused fires. This caused some to go out midflight. Some exploded and took out neighboring ones. Communication to the flight computers and the TVC was severed due to the fires.

Also the second flight was because the oxygen filtration system for the engines got clogged (maybe just for one engine) with some debris. We don't know what the debris was, but it's probable that the sloshing environment caused something to get dislodged and clog the filter. When one engine went out it had a cascade effect on several others. SpaceX has reported this on their website.

[–]crazyarchon 1 point2 points  (19 children)

Sorry to disappoint you but the flight is down to some 65min, so about 2/3rds of an orbit. Not sure if going through the regular steps of testing what a rocket needs to do is pushing the envelope but then again it always comes down to the envelope itself. Also not that what they are testing is easy at all, just wait for actual envelope pushing (thinking of some chop sticks) to actually use the metaphor.

[–]ergzay 9 points10 points  (11 children)

Orbit is defined by velocity and trajectory you achieve, not how long you're in that orbit.

[–]7473GiveMeAccount 1 point2 points  (1 child)

true of course, but they're still not entering orbit

their trajectory at MECO will probably have ~200km apogee, and ~50km perigee, well within the atmosphere

100km perigee or thereabout is a sensible cutoff for entering orbit imo. at 50km you can't complete a single orbit no matter what, drag will pull you back down

the *energy* of the ship will still be very close to that of a proper orbit of course, so the trajectory*is* representative of orbit from a test perspective

[–]ergzay 0 points1 point  (0 children)

their trajectory at MECO will probably have ~200km apogee, and ~50km perigee, well within the atmosphere

https://en.wikipedia.org/wiki/Transatmospheric_orbit

[–]crazyarchon -1 points0 points  (2 children)

Yes, if your trajectory brings your perigee above the surface one has achieved orbit, but the only thing we know is that the flight will be ~30% shorter, which makes the assumption more reasonable that they again are not going for an orbit but rather a longer hop. But its really all just speculation.

[–]Bensemus 1 point2 points  (1 child)

They are going for a transatmospheric orbit. Apogee above 100km, perigee within the atmosphere. This is so it’s impossible to get stuck in space and reenter uncontrolled.

[–]crazyarchon -2 points-1 points  (0 children)

Neat, what’s your source for that? Also, Perigee would also be above karman line, but lower than LEO. At least according to transatmospheric orbit definition. There the atmosphere is still enough to rapidly decay the orbit. Though without action like a controlled burn, the reentry could be uncontrolled, though that is obviously not what they are going for.

[–]Dont_Think_So 1 point2 points  (6 children)

If you care about the difference between 100% of the energy required to reach orbit and 98% of the energy required to reach orbit, might I kindly suggest you go touch some grass.

[–]Martianspirit 3 points4 points  (0 children)

98% of the energy required to reach orbit

Pretty sure it is way closer to 100% than mere 98%.

[–]crazyarchon -1 points0 points  (4 children)

I am not sure how you get to those percentages.

[–]Dont_Think_So 1 point2 points  (3 children)

Starship gets to orbital velocity, which requires ~10 km/s delta v. The only reason it isn't orbital is because it doesn't perform a circularization burn to bring the perigee outside the earth's atmosphere, which requires ~1 km/s. Energy goes with velocity squared, so 99% of the energy is spent getting to orbital velocity, 1% energy is spent turning it into a circular orbit.

In practice it's worse than that, because the rocket equation says that fuel requirements go with edelta v, so in fact a tiny fraction of the total fuel is used to circularize. On the scale of keeping the engines on for a few extra seconds in a minutes-long flight.

[–]crazyarchon 1 point2 points  (2 children)

Thank you for that detailed summary of your napkin calculation. So you went through all this just to tell me to touch grass because I dared to point out that their flight path is ~1/3rd shorter than their initial two test flights? One might want to advise you to maybe go outside and touch some grass. I wouldn’t say that, bug someone might do that.

[–]Dont_Think_So 0 points1 point  (1 child)

I'm saying that it's splitting hairs, no one who knows anything about this stuff cares about the difference. It's a WeLl AkShuAllY kind of thing. If you do really care about this difference, maybe go find something more important to argue about.

[–]crazyarchon 0 points1 point  (0 children)

But… you started to argue with me about the semantics. I just made the observation that we don’t know that they’ll actually reach orbit because the are only planning 2/3rds of the orbital time. That is a fact. You are the one putting your foot down that is actually close to an orbit (but still not), while simultaneously arguing that I should argue about something more important, even if I care about this deeply.

[–]dingo1018 5 points6 points  (2 children)

Where can I bet my pocket money on a successful third time lucky flight? (Actually a serious question)

[–]Steve490 1 point2 points  (0 children)

Can find your exact request, but here are markets for if it will achieve orbit this year and if the launch will happen by a certain date.

https://kalshi.com/markets/spacexorbit/starship-in-orbit

[–]Fredasa 2 points3 points  (0 children)

Gotta imagine that if test flights are going to have 4 to 5 months separating them until Cape Canaveral is operational, then yeah, SpaceX is going to feel the pressure to accomplish more than simply "more of the last flight's wish list."