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Starship's Third Flight Test [video]

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Re: Starship's Third Flight Test [video]

#301

Post by usrusr »

dotnet00 wrote: post #157
johnyzee wrote: post #138

Earlier quoted context omitted.

Yeah, breaking up in-air during re-entry (at 65 km going by last telemetry) seems like a potential big issue to fix.

OP's point is that the tests become a bit cheaper and a bit easier to get licenses for since they can get to orbit and can deploy Starlinks. The reentry problems of course have to be fixed, but the FAA mishap investigation will involve fewer delays, just like how Falcon 9 was able to keep flying, attempting landings without having to wait for a mishap investigation to finish every time a landing failed.

Iirc F9 had its main challenge in that final suicide burn. Usually the boosters made it there just fine and then "only" failed to get the parameters aligned just right.

Based on what we saw today, the main chokepoint for Starship might be right in that hot reentry telemetry blind spot. Debugging without logs.

Re: Starship's Third Flight Test [video]

#302

Post by numpad0 »

lupusreal wrote: post #296
numpad0 wrote: post #248

Earlier quoted context omitted.

IIUC real launchers do a single burn to orbit because S2 TWR is not very high and relight is finicky. Launchers that has relightable S2 and/or hypergolic S3 routinely do circularization burns. There are reasons "apogee" is more recognized word than "apoapsis".

> There are reasons "apogee" is more recognized word than "apoapsis". What are you getting at? The -gee suffix means Earth. Apogee is apoapsis of an orbit around Earth. People playing KSP speak of apoapsis because Kerbin isn't Earth.

IRL they always did and therefore discussed "apogee kicks" after payload release into elliptical transfer orbit(literally GTO). That's where I'm getting at.

If you think about it, there can't be an ellipse that intersects a circle while also being fully encompassed by the latter. That's to say the periapsis can't be higher than the maneuver altitude that the off-apsis burn takes place as the other guy is suggesting.

On real rockets they add small shelf-stable stage such as the spinny boi Star-48 or the notoriously narcoleptic Fregat, inside fairings between S2 payload interface to actual payload, or let the payload pull itself into the final orbit at a great expense.

Yes, you can keep the S2 burning all the way to Ap and then burn at -45deg at Ap to deform the ellipse back into a circle, or fly a by the book gravity turn trajectory, but that's not the most energy efficient insertion, only what are situationally beneficial when there is land below and acceleration is limited.

Re: Starship's Third Flight Test [video]

#303

Post by bdamm »

Laremere wrote: post #268
Laremere wrote: post #219

Earlier quoted context omitted.

My bet on the re-entry failure is that they have really poor attitude control. They definitely had some, but you can also see at different points that the plasma was shifting directions. At T+46, it was doing a spin as the first plasma started to show. At T+47, it was going down on the edge of the heat shields. At T+47:40 it appears to be going down engine first. Moreover, I'm guessing the reason they skipped the moc…

I just noticed that I typed "Tim Todd" instead of "Tim Dodd". It's past the edit period so I shall forever live with this shame. In my defense, I was on 5 hours of sleep so I could watch the launch.

You are a contemporary yet timeless sort of gentleman. Well done.

Re: Starship's Third Flight Test [video]

#304

Post by Retric »

93po wrote: post #293
bane wrote: post #280

Earlier quoted context omitted.

Now do the same calculation in units of hubble space telescope and james webb space telescope masses. Then look at expected reusable launch cost and figure out how many HSTs or JWSTs we could have put in orbit for the same cost.

JWST would also be incredibly less expensive if it didn't have to do the very complex folding required by smaller rockets

JWST would still have been an extremely novel and therefore expensive on Spaceship. We just don't build anything that uses that kind of sun shield or those sensors etc and everything needs to work on one shot, thus serious engineering effort.

Re: Starship's Third Flight Test [video]

#305

Post by avmich »

mgiampapa wrote: post #288
jkjkjjjkjkj wrote: post #281

Earlier quoted context omitted.

Well, the second stage definitely needs to survive re-entry if it wants to carry passengers. But it seems to work as-is for orbital cargo.

Passenger rating isn't even in the cards for Starship for a long time. You ride to LEO on a Falcon-9 with a proven track record for the foreseeable future.

"Foreseeable" is roughly "five years"? Starship HLS (Human Landing System) is currently planned to land on the Moon, with people, in 2026. It may very well slip a year, two or three - but landing on the Moon this decade still seems quite possible. Or you consider "passengers" different enough than "crew"?

Re: Starship's Third Flight Test [video]

#306

Post by dotnet00 »

usrusr wrote: post #301
dotnet00 wrote: post #157

Earlier quoted context omitted.

OP's point is that the tests become a bit cheaper and a bit easier to get licenses for since they can get to orbit and can deploy Starlinks. The reentry problems of course have to be fixed, but the FAA mishap investigation will involve fewer delays, just like how Falcon 9 was able to keep flying, attempting landings without having to wait for a mishap investigation to finish every time a landing failed.

Iirc F9 had its main challenge in that final suicide burn. Usually the boosters made it there just fine and then "only" failed to get the parameters aligned just right. Based on what we saw today, the main chokepoint for Starship might be right in that hot reentry telemetry blind spot. Debugging without logs.

It sounded like they might have had flight data recorders on-board which might have survived through reentry with telemetry. If so, they'd have some logs, but yes, figuring out reentry will likely be the main challenge for now, not only is it hard to debug, even getting to it requires everything else to go more or less perfectly.

Re: Starship's Third Flight Test [video]

#307

Post by cruffle_duffle »

namaria wrote: post #9

I was just watching Spacex official stream and at ignition they switched to Musk hawking cryptocurrency. What just happened?? edit: wild I just realized take off is 50 minutes from now... what had I been watching?? they did a countdown and there was ignition... was that a time wrap? Am I going insane? edit2: @spacex034 is not @spacex... today I learned...

Dude, we encountered that yesterday. Somebody really figured out how to successfully pretend to be a spacex livestream! It was super weird, right?

Re: Starship's Third Flight Test [video]

#308

Post by grecy »

BenoitP wrote: post #207
grecy wrote: post #191

Earlier quoted context omitted.

From a safety perspective, how does that work? This is obviously a test, and safe to say the vehicle was out of control and not entirely predictable. I realize they wouldn't fly into the actual predicted landing area, but just being close must be a risk. Would the flight crew on that plane literally be scanning the sky above them to make sure they're not in the direct path of whatever comes down at whatever speed?

I guess some risk analysis can be made with the plane's and Starship's cross-section. Let say they are cubes of 30m each. The expected area where they might both be present to be a 5km square. That's a 0.000025 chance of collision at most; and I suppose the plane is away from the center of the expected Starship Gaussian. I'd personally ride in that plane and risk that, even to just to get a glimpse of the reentry.

that.... makes a lot of sense. Thanks.

Somehow I was thinking it was super risky to be in the general area, but your numbers show that is clearly no the case.

Re: Starship's Third Flight Test [video]

#309

Post by DarmokJalad1701 »

2OEH8eoCRo0 wrote: post #284
bane wrote: post #258

Earlier quoted context omitted.

Here's a fun thought, how many Starship launches would it take to put the equivalent mass of the ISS up in the same orbit?

How many launches are required to land on the Moon?

Depends on what lunar lander hardware is being used. If we were using Apollo hardware:

Apollo LM: 16 metric tons (landing about 5 tons on the moon)

Apollo CSM: 29 metric tons

The third stage of the Saturn V, called the S-IVB, (which was used for the trans-lunar injection burn) weighed 123 tons - however this was also used to get into the initial orbit.

Starship can launch 150 tons to LEO in reusable mode or ~200 mt when expended. The Saturn V was able to launch 141 tons to LEO. So it should theoretically be possible for Starship to launch an LM+CSM stack with an S-IVB with enough fuel for a trans-lunar injection burn. Then fly the rest of the mission as in Apollo.

Or we can refuel the Starship a few times in LEO using a bunch of re-usable flights and land 100 tons of payload on the lunar surface. The latter is probably cheaper and simpler at this point.

Re: Starship's Third Flight Test [video]

#310

Post by DarmokJalad1701 »

golol wrote: post #189
DarmokJalad1701 wrote: post #167

Earlier quoted context omitted.

> They can't leave the Starship up in orbit, and where it reenters needs to be controlled. Why? Plenty of boosters re-enter uncontrolled and burn up all the time.

Ok so they could leave Starship in orbit and launch payloads like that. The idea however is to launch payloads WHILE testing reentry and landing. This requires an engine relight in orbit.

> WHILE testing reentry and landing.

> This requires an engine relight in orbit.

The latter is part of the test at this point of development

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