The blunt body used for ballistic entry for Mercury and Gemini were dynamically stable. After retrofire the spacecraft only needed to present the heat-shield to the velocity vector for stable ballistic entry (high g's required form fitting seats). The conical shape used for Apollo, Orion and Starliner utilize an offset cg for lifting entry, cross-range and flight direction. Upon entry to maintain attitude it must use active RCS either under computer or pilot guidance. The offset cg require offset drogues for stability as well If a total RCS failure occurs the spacecraft will begin to roll about its vertical axis altering its AoA in an "oscillating roll-coupling" fashion that will end up it what has been described as eventually tumbling through the atmosphere. The result is a bad day...
The blunt body used for ballistic entry for Mercury and Gemini were dynamically stable. After retrofire the spacecraft only needed to present the heat-shield to the velocity vector for stable ballistic entry (high g's required form fitting seats). The conical shape used for Apollo, Orion and Starliner utilize an offset cg for lifting entry, cross-range and flight direction. Upon entry to maintain attitude it must use active RCS either under computer or pilot guidance. The offset cg require offset drogues for stability as well If a total RCS failure occurs the spacecraft will begin to roll about its vertical axis altering its AoA in an "oscillating roll-coupling" fashion that will end up it what has been described as eventually tumbling through the atmosphere. The result is a bad day...
In other words, entry without any form of propulsive attitude control is pretty much a death sentence, right?
So--and I apologize if I'm sounding a bit obsessed with this--why would you insert a crewed spacecraft into 72x181 unless you had to for performance reasons that were constrained by the ascent trajectory?
You have a point if you're implying a different trajectory would allow abort to orbit and time to get the thrusters working if they failed completely, but I think it's important to point out there is redundancy built into the thruster system. A complete failure is highly unlikely, as is a need for an abort of any kind in the first place. This thread has gone on and on painting a very bleak picture that has only a remote chance of occurring. It helped me to listen again to the astronauts' viewpoint from the post-launch conference. They are more than confident. And before I post the link that begins with their 2 minutes speaking (and later answering some reporters' questions), I would also like to point out that the simulation that was quoted earlier that only one astronaut passed took place not in the spring of 2019, but the spring of 2018, much earlier in the astronauts' training.
https://www.youtube.com/watch?v=NpQlxN4xbKM?t=790
You have a point if you're implying a different trajectory would allow abort to orbit and time to get the thrusters working if they failed completely, but I think it's important to point out there is redundancy built into the thruster system. A complete failure is highly unlikely, as is a need for an abort of any kind in the first place. This thread has gone on and on painting a very bleak picture that has only a remote chance of occurring. It helped me to listen again to the astronauts' viewpoint from the post-launch conference. They are more than confident. And before I post the link that begins with their 2 minutes speaking (and later answering some reporters' questions), I would also like to point out that the simulation that was quoted earlier that only one astronaut passed took place not in the spring of 2019, but the spring of 2018, much earlier in the astronauts' training.
https://www.youtube.com/watch?v=NpQlxN4xbKM?t=790
Ah, but if it's highly unlikely to have a complete thruster failure (and I agree that it is unlikely), then you can deorbit from a stable orbit--something like 150x181. That saves you not only from the remote chance of a physical thruster failure, but also from some avionics-based goat rodeo that takes the system down for, oh, let's say about 45 minutes--just long enough that you'd reenter out of control if you were in the 72x181.
Furthermore, you still have virtually the same access to an early abort if something bad happens where time to get back on the ground is of the essence--it just costs you 25 m/s of RCS or OMAC, which is pretty trivial in the grand scheme of things.
The only case I can think of where the 72x181 saves you is the case where, for some reason, you run through several hundred m/s of delta-v doing some hideous attitude control problem, but manage to get the problem under control with just enough prop to control reentry but not the extra 25 m/s needed to initiate the deorbit. That's... possible... but I can think of a lot more bad things that would cause you to reenter out of control from 72x181 than would strand you in 150x181.
Now, to be fair, we just witnessed a hideous attitude control problem. But we also exited that problem with not only enough prop to deorbit, but also enough to do a cheesy perigee-raise. Which kinda bolsters my point.
An example of what could happen to a capsule like Starliner (shape wise), in this case Orion, in case of zero control:
https://www.youtube.com/watch?v=2RbbSGrO_tY?t=120
Albeit this is at relatively low altitude compared to an orbital re-entry, it is quite clearly not stable.
This also got me thinking, what if the Starliner, with its OFT software, would have had to abort? if the same issue would have manifested in an abort scenario too, things could have ended much worse.
An example of what could happen to a capsule like Starliner (shape wise), in this case Orion, in case of zero control:
https://www.youtube.com/watch?v=2RbbSGrO_tY?t=120
Albeit this is at relatively low altitude compared to an orbital re-entry, it is quite clearly not stable.
This also got me thinking, what if the Starliner, with its OFT software, would have had to abort? if the same issue would have manifested in an abort scenario too, things could have ended much worse.
An example of what could happen to a capsule like Starliner (shape wise), in this case Orion, in case of zero control:
https://www.youtube.com/watch?v=2RbbSGrO_tY?t=120
Albeit this is at relatively low altitude compared to an orbital re-entry, it is quite clearly not stable.
This also got me thinking, what if the Starliner, with its OFT software, would have had to abort? if the same issue would have manifested in an abort scenario too, things could have ended much worse.
An example of what could happen to a capsule like Starliner (shape wise), in this case Orion, in case of zero control:
https://www.youtube.com/watch?v=2RbbSGrO_tY?t=120
Albeit this is at relatively low altitude compared to an orbital re-entry, it is quite clearly not stable.
This also got me thinking, what if the Starliner, with its OFT software, would have had to abort? if the same issue would have manifested in an abort scenario too, things could have ended much worse.
Once a capsule shaped like this (Apollo, Orion, Starliner) starts tumbling like this, parachute deploy is *not* going to save it. The shroud lines will either be ripped from their anchors or become badly entangled in the spacecraft itself, or both. Stabilization MUST occur first thru thruster control. I hadn't given it much thought before but now I am wondering why thruster control wasn't used to gain stabilization and why subsequent parachute deploy did not occur. In the IFA tests of Apollo, lofted by the Little Joe LV, both were employed and demonstrated to be functional. https://tinyurl.com/kg9pqsa That was a requirement to sign off on the Apollo IFA capability. Why not for Orion? Apollo was required to demonstrate IFA capability. Why wasn't it made a requirement for both Dragon and Starliner? Hindsight is always 20/20 but still, why not? What were they thinking? Just thinking out loud. But of course that is a subject for a different thread, so let's not go there, here.
An example of what could happen to a capsule like Starliner (shape wise), in this case Orion, in case of zero control:
https://www.youtube.com/watch?v=2RbbSGrO_tY?t=120
Albeit this is at relatively low altitude compared to an orbital re-entry, it is quite clearly not stable.
You have a point if you're implying a different trajectory would allow abort to orbit and time to get the thrusters working if they failed completely, but I think it's important to point out there is redundancy built into the thruster system. A complete failure is highly unlikely, as is a need for an abort of any kind in the first place. This thread has gone on and on painting a very bleak picture that has only a remote chance of occurring. It helped me to listen again to the astronauts' viewpoint from the post-launch conference. They are more than confident. And before I post the link that begins with their 2 minutes speaking (and later answering some reporters' questions), I would also like to point out that the simulation that was quoted earlier that only one astronaut passed took place not in the spring of 2019, but the spring of 2018, much earlier in the astronauts' training.
https://www.youtube.com/watch?v=NpQlxN4xbKM?t=790
Ah, but if it's highly unlikely to have a complete thruster failure (and I agree that it is unlikely), then you can deorbit from a stable orbit--something like 150x181. That saves you not only from the remote chance of a physical thruster failure, but also from some avionics-based goat rodeo that takes the system down for, oh, let's say about 45 minutes--just long enough that you'd reenter out of control if you were in the 72x181.
Furthermore, you still have virtually the same access to an early abort if something bad happens where time to get back on the ground is of the essence--it just costs you 25 m/s of RCS or OMAC, which is pretty trivial in the grand scheme of things.
The only case I can think of where the 72x181 saves you is the case where, for some reason, you run through several hundred m/s of delta-v doing some hideous attitude control problem, but manage to get the problem under control with just enough prop to control reentry but not the extra 25 m/s needed to initiate the deorbit. That's... possible... but I can think of a lot more bad things that would cause you to reenter out of control from 72x181 than would strand you in 150x181.
Now, to be fair, we just witnessed a hideous attitude control problem. But we also exited that problem with not only enough prop to deorbit, but also enough to do a cheesy perigee-raise. Which kinda bolsters my point.
Exactly
And active deorbiting would let the mission choose the location, rather than falling into the remote South Indian Ocean.
And saying it’s OK because there is a backup, in this case astronauts who have to feel confident in their abilities to solve almost any problem, is the path to high risk Chuck and others discuss above.
In short, people here have said why launching suborbital may be acceptable, but there is still no clear way it could be preferable. It still doesn’t make sense.
QuoteFirst and foremost, that 407x407 orbit assumes the usual lofted trajectory, which the N22 can't fly and meet the continuous abort requirement for a crewed trajectory. Hence the depressed trajectory.The 13.25 tonne payload comes directly from an "Atlas V Starliner" brochure, which I believe would assume a crew ascent trajectory.
- Ed Kyle
a 51QuoteFirst and foremost, that 407x407 orbit assumes the usual lofted trajectory, which the N22 can't fly and meet the continuous abort requirement for a crewed trajectory. Hence the depressed trajectory.The 13.25 tonne payload comes directly from an "Atlas V Starliner" brochure, which I believe would assume a crew ascent trajectory.
- Ed KyleThere has never been a 522 Atlas launch but looking up the Atlas V 521 Specs we see 13.4 tons into LEO at a 28 degree inclination. ISS is around 51-degree inclination to accommodate Soyuz.. That means more fuel to go from 28 to 51 degrees. The N22 has the extra RL10 to get up to 51 degrees in time to chase ISS. Then the Starliner OMT's job is to change the perigree and apogee.
I think the insertion orbit was the best Atlas V can do given the 3.5 g maximum. Otherwise, they could add another SLB.
Thank you for that clear and concise summary, Comga, and for acknowledging your alliance with RadicalModerate, whom I don't know or understand as well. Maybe he is just trying to mix in some respect for Boeing's decision in order to get heard, but I've been having some of the same difficulty seeing what he wants that '1' had, so I know it's not because I have lesser knowledge.
For example, in Rad's last 2 paragraphs, he acknowledges that Boeing's 72x181km trajectory would work for the same anomaly that occurred, so how does that "bolster his point" that a 150x181km trajectory would be more advisable?
An early mission planners guide gave Atlas 522 (using DEC) at more than 15 tonnes to 185 km circular x 28.5 deg. Now ULA says that N22, which is designed for only one purpose - flying CST-100 on a depressed trajectory, can do more than 13 tonnes to 400 km x 51.6 deg. No one wants to believe the source, for some reason, despite multiple pieces of corroborating evidence listed on this very thread.
- Ed Kyle
Soon after the spacecraft was launched, it went off track because a clock was not set correctly, failing to reach the correct orbit and rendezvous with the International Space Station. The botched Starliner mission was a crushing blow to company morale, with employees desperate for good news after a difficult year.
Yet Mr. Muilenburg, who updated the board about the mission, remained positive and emphasized what had gone right, according to three people with knowledge of the matter. His response was seen as another sign of his being overly optimistic about the company’s challenges.
An example of what could happen to a capsule like Starliner (shape wise), in this case Orion, in case of zero control:
https://www.youtube.com/watch?v=2RbbSGrO_tY?t=120
Albeit this is at relatively low altitude compared to an orbital re-entry, it is quite clearly not stable.
This also got me thinking, what if the Starliner, with its OFT software, would have had to abort? if the same issue would have manifested in an abort scenario too, things could have ended much worse.
Once a capsule shaped like this (Apollo, Orion, Starliner) starts tumbling like this, parachute deploy is *not* going to save it. The shroud lines will either be ripped from their anchors or become badly entangled in the spacecraft itself, or both. Stabilization MUST occur first thru thruster control. I hadn't given it much thought before but now I am wondering why thruster control wasn't used to gain stabilization and why subsequent parachute deploy did not occur. In the IFA tests of Apollo, lofted by the Little Joe LV, both were employed and demonstrated to be functional. https://tinyurl.com/kg9pqsa That was a requirement to sign off on the Apollo IFA capability. Why not for Orion? Apollo was required to demonstrate IFA capability. Why wasn't it made a requirement for both Dragon and Starliner? Hindsight is always 20/20 but still, why not? What were they thinking? Just thinking out loud. But of course that is a subject for a different thread, so let's not go there, here.
In the Orion IFA video above, RCS jets were firing wildly in an attempt to stabilize the capsule, but not succeeding. Looked like the last part, someone programmed the RCS jets to... lets see how fast we can get this to spin mode