ULA may never reveal how they 'messed up', as you describe it, but the interface belongs to Atlas. If that interface is prone to error, then yes, there is a problem with Atlas. If I was working on DC for CRS-2, I'd be checking every line of code that talks to that interface and reconfirming each 'coefficient' (whatever that actually means), it's name, definition, location, size, endianness, range, and while at it, I'd send a high level request to insure that the spec I was working on was actually the final spec. If I was testing the interface, I wouldn't settle for an emulator or a bench system, I'd schedule runs on the actual flight hardware. If I was Boeing, I'd be looking at that interface in order to understand why it was easily misinterpreted and resulted in a mission that failed to meet its objectives.
Please stop making things up. ULA did not mess up, as you are trying to imply. What does that even mean: "the interface belongs to Atlas". It's not prone to error and there is not a problem with Atlas. You seem to want to create an issue on the LV side where there isn't one. The spacecraft was separated into the exact orbit the customer specified.
There are Interface Control Documents (ICD) that specified all the requirements. There are also a Mechanical ICD that specifies the hardware interface requirements (assuming ULA provides the sep system) and an Electrical ICD to specify things like connectors, pins, commands, etc. All documents are signed by both parties and very clearly describe how the verifications of the requirements are to be met.
Why don't you wait until the postflight analysis is complete before you start negatively speculating (or wishing) that ULA did something wrong.
I agree that this is not a ULA problem, but I am curious how robust the interface is. Do you know its details?
My last true aerospace experience was in the early days of the Shuttle, and back then there were interfaces that required raw addresses to be propagated from the MDMs into the software build, and raw addresses from the build into external ground- and crew-control systems.
It's now obviously almost 40 years later, and there's plenty of both hardware and software technology that would obviate that kind of thing in a new system. But Atlas V is really a bit more than 20 years old, if you count the design process (where such things are decided), so I'm not sure of the sophistication of the interface.
If you do a maintenance build on the A5 avionics and it moves stuff around in memory a bit, an interface that says "get me the value of the object labelled 'MET #2'" is pretty much immune to all but an actual bug being introduced. On the other hand, a new build when the interface is "get me the 32-bit value that resides at 0x056789ab" requires perfect config control between the A5 avionics team and the Starliner team.
ULA may never reveal how they 'messed up', as you describe it, but the interface belongs to Atlas. If that interface is prone to error, <snip>
I'm going to speculate that the crew loading issue being managed by the flat trajectory has nothing to do with the acceleration provided by the dual Centaurs, but rather it is done because if the trajectory was not flat, but more lofted, a crew abort would see the capsule enter at a much steeper angle where it could not use it's aerodynamic lift to manage the "g" loading during descent.
2) I think this is the one you're talking about: The more serious one is because they can't loft as much as the A5 usually does. If they do and then have a late-burn CCB failure or a failure any time with the DEC, the Starliner will reenter very steeply and slam back into the atmosphere at unsurvivable acceleration and thermal loads. That's what requires the depressed trajectory, which keeps all aborts in a reasonable reentry corridor.
2) I think this is the one you're talking about: The more serious one is because they can't loft as much as the A5 usually does. If they do and then have a late-burn CCB failure or a failure any time with the DEC, the Starliner will reenter very steeply and slam back into the atmosphere at unsurvivable acceleration and thermal loads. That's what requires the depressed trajectory, which keeps all aborts in a reasonable reentry corridor.
That's related to my thought. At reentry you can't have the capsule skipping across the surface of the lower atmosphere.
2) I think this is the one you're talking about: The more serious one is because they can't loft as much as the A5 usually does. If they do and then have a late-burn CCB failure or a failure any time with the DEC, the Starliner will reenter very steeply and slam back into the atmosphere at unsurvivable acceleration and thermal loads. That's what requires the depressed trajectory, which keeps all aborts in a reasonable reentry corridor.
That's related to my thought. At reentry you can't have the capsule skipping across the surface of the lower atmosphere.If I understand it correct, the capsule would not skip, but it would manage skimming on the upper atmosphere by managing its lift & drag to bleed energy at high altitude & low g loading. It would not be able to do this if it was on a steep ballistic trajectory dictated by a more lofted profile.
So I'm stumped why they did this. Any thoughts?
So I'm stumped why they did this. Any thoughts?Once around automatic safe abort. Plain and simple.
- Ed Kyle
So I'm stumped why they did this. Any thoughts?Once around automatic safe abort. Plain and simple.
- Ed Kyle
If Starliner doesn't do the OIB after the Centaur drops it off, it doesn't go once around.
It is suborbital and comes down in the Indian Ocean off the SW coast of Australia.
Or did I misunderstand your post?
I can appreciate the blackout zone argument, however I'm not groking the load limits statement. Seems to me that 2 Centaurs should provide a gentle ascent. Even at max thrust it shouldn't exceed 3 g's
Maybe this link has your answer:
https://spaceflightnow.com/2019/12/19/starliner-test-flight-to-use-special-atlas-5-configuration-unusual-launch-trajectory/
Basically it comes down to crew loading and avoidance of blackout zones in the North Atlantic where the capsule would possibly not be able to be recovered.
I can appreciate the blackout zone argument, however I'm not groking the load limits statement. Seems to me that 2 Centaurs should provide a gentle ascent. Even at max thrust it shouldn't exceed 3 g's
Right. Not all the way around. Safe abort to Indian Ocean.
- Ed Kyle
Right. Not all the way around. Safe abort to Indian Ocean.
- Ed KyleDo they have rescue assets placed there or nearby? Wondering how long the capsule is good for if it aborts and has to await assets to travel some distance.
But that still doesn't answer the question. The article gives several reasons for the trajectory and none are the obvious motivation.
One is to prevent aborting into the hostile, far north Atlantic Ocean, where retrieval, rescue, would be long and arduous.
But the Instantaneous Impact Point (IIP) still crosses that regions. In fact, as a vehicle approaches orbital speed, the IIP begins to race around the globe, spending less and less time crossing the various regions. Going into a suborbital trajectory means the IIP never dissappears, but stays on the ground for the entire half hour until orbital insertion.
Minimizing this interval requires maximzing the acceleration, but this is something the weak RL-10's, with their "45,000 lbs of thrust" can't do.
(The Merlin Vacuum engines, with its 200,000 lbs of vacuum thrust, generates significantly higher acceleration. In fact, it has to be throttled to stay under acceleration limits, while the article says that even at the end, the Centaur is accelerating Starliner at roughly 1 g.)
Another possible reason is to maximize the "comfort" of the astronauts in an abort. But comfort is not the main goal. Survival is. How is it necessary to limit abort reentry to 3.5 g's, in an event with the probability of about one in a hundred launches, when NASA routinely accepts the risk of a ballistic reentry in Soyuz, with its 8 to 10 g's?
(Dragon-2 has a much more lofted trajectory, and with it's steeper sidewalls much have a higher ballistic coefficient, and much greater reentry forces, but NASA has found those abort modes acceptable.)
Another stated reason is that the Centaur will naturally reenter after half an orbit. But if any Centaur has failed to perform a commanded deorbit burn, it must have been long, long ago.
Someone asked about the 1.5 tons of fuel left in the Centaur after shutdown. A colleague who deals extensively with ULA says that this is standard operating procedure for Atlas V. It is part of the conservatism that makes this rocket so reliable. But it does leave Starliner with all that fuel plus the abort fuel that has to be burned off.
(A fraction of this fuel could put Starliner in a stable orbit.)
The last reason is that Shuttle launched in this same manner. This brought down the 78,000 lb External Tank safely in the Indian Ocean. But it also relied on the Shuttle's OMS engines to get to orbit. So when the Starliner has a crew on board it will operate just like the Shuttle. If the automatic controls fail to start the orbit insertion burns, the crew will.
This could be the real reason: because Shuttle did it this way. (But the Shuttle never flew without crew.)
Boeing has a good feel for just how much innovation NASA could tolerate. Pusher LAS engines and airbag desert landing were judged to be the limit. Taking the LH2/LOX tanks to orbit may have been judged to be beyond it.
So I'm stumped why they did this. Any thoughts?Once around automatic safe abort. Plain and simple.
- Ed Kyle
And would not be able to do that using an initial insertion orbit like 150x181 that RadicalModerate suggested?