-
#480
by
Comga
on 04 Jan, 2020 00:08
-
Tumble = LOC
This has happened to a Russian cosmonaut.
-
#481
by
TheRadicalModerate
on 04 Jan, 2020 06:17
-
I have a serious question:
From the standpoint of the rocket equation, it is inefficient to bring modest Isp fuel, like that for the OMAC engines, using high Isp fuel like the LH2/LOX for Centaur.
Would it be possible to burn, say, a pair of 1,500 lb thrust OMAC engines to augment the 45,000 lb thrust RL-10 pair?
This could get rid of the unwanted fuel mass and save enough prop for the Centaur to do a deorbit burn. (and wind up with the same fuel margin as the reference mission)
Lockheed looked into using the LAS engine on Orion to augment the SLS. However, being solid launch abort engines, they could not be throttled, and the resulting massive thrust would have caused such a change in load paths that enormous structural redesign would have been required. In the end this idea was dropped.
But a pair of OMAC engines would be <7% of the thrust of the DEC, and the load on the Centaur would always remain positive, in compression.
The LAS engines are live, of course, before and during launch, but does this mean the OMAC engines are enabled or disabled? Do they fire during an abort for control or not?
The fuel becomes excess after MECO, where the LAS doesn’t have to start at a standstill, plow through the air at MaxQ, it outrun a nearly empty first stage. Before dropping the aeroskirt seems to be the perfect time to burn it thru the OMACs.
Just as with the escape tower idea, the rocket equation is not your friend. If OMACs are dragging around a half-full Centaur as well as the Starliner, the amount of delta-v they generate is pretty small, because the mass ratio is small.
-
#482
by
eeergo
on 04 Jan, 2020 10:45
-
Tumble = LOC
This has happened to a Russian cosmonaut.
Which one?
-
#483
by
Svetoslav
on 04 Jan, 2020 11:32
-
Perhaps he means Volynov. He experienced tumbling on reentry.
-
#484
by
ZachS09
on 04 Jan, 2020 11:37
-
Perhaps he means Volynov. He experienced tumbling on reentry.
Yet he survived the reentry, albeit with broken teeth upon touchdown due to a soft-landing rocket malfunction.
-
#485
by
Comga
on 04 Jan, 2020 13:44
-
I have a serious question:
From the standpoint of the rocket equation, it is inefficient to bring modest Isp fuel, like that for the OMAC engines, using high Isp fuel like the LH2/LOX for Centaur.
Would it be possible to burn, say, a pair of 1,500 lb thrust OMAC engines to augment the 45,000 lb thrust RL-10 pair?
This could get rid of the unwanted fuel mass and save enough prop for the Centaur to do a deorbit burn. (and wind up with the same fuel margin as the reference mission)
Lockheed looked into using the LAS engine on Orion to augment the SLS. However, being solid launch abort engines, they could not be throttled, and the resulting massive thrust would have caused such a change in load paths that enormous structural redesign would have been required. In the end this idea was dropped.
But a pair of OMAC engines would be <7% of the thrust of the DEC, and the load on the Centaur would always remain positive, in compression.
The LAS engines are live, of course, before and during launch, but does this mean the OMAC engines are enabled or disabled? Do they fire during an abort for control or not?
The fuel becomes excess after MECO, where the LAS doesn’t have to start at a standstill, plow through the air at MaxQ, it outrun a nearly empty first stage. Before dropping the aeroskirt seems to be the perfect time to burn it thru the OMACs.
Just as with the escape tower idea, the rocket equation is not your friend. If OMACs are dragging around a half-full Centaur as well as the Starliner, the amount of delta-v they generate is pretty small, because the mass ratio is small.
No, it is my friend
It is precisely because it is NOT like the escape tower and the delta-V would be small that it could work.
The OMACs wouldn’t be “dragging” the Centaur as much as lightening it’s load.
Like the Electron dropping batteries halfway through the second stage burn, there is a mass multiplier. A ton of fuel dumped early means more than a ton of extra propellants for Centaur, enough to get to a stable orbit AND do a deorbit burn.
-
#486
by
John Santos
on 04 Jan, 2020 14:40
-
I have a serious question:
From the standpoint of the rocket equation, it is inefficient to bring modest Isp fuel, like that for the OMAC engines, using high Isp fuel like the LH2/LOX for Centaur.
Would it be possible to burn, say, a pair of 1,500 lb thrust OMAC engines to augment the 45,000 lb thrust RL-10 pair?
This could get rid of the unwanted fuel mass and save enough prop for the Centaur to do a deorbit burn. (and wind up with the same fuel margin as the reference mission)
Lockheed looked into using the LAS engine on Orion to augment the SLS. However, being solid launch abort engines, they could not be throttled, and the resulting massive thrust would have caused such a change in load paths that enormous structural redesign would have been required. In the end this idea was dropped.
But a pair of OMAC engines would be <7% of the thrust of the DEC, and the load on the Centaur would always remain positive, in compression.
The LAS engines are live, of course, before and during launch, but does this mean the OMAC engines are enabled or disabled? Do they fire during an abort for control or not?
The fuel becomes excess after MECO, where the LAS doesn’t have to start at a standstill, plow through the air at MaxQ, it outrun a nearly empty first stage. Before dropping the aeroskirt seems to be the perfect time to burn it thru the OMACs.
Just as with the escape tower idea, the rocket equation is not your friend. If OMACs are dragging around a half-full Centaur as well as the Starliner, the amount of delta-v they generate is pretty small, because the mass ratio is small.
No, it is my friend
It is precisely because it is NOT like the escape tower and the delta-V would be small that it could work.
The OMACs wouldn’t be “dragging” the Centaur as much as lightening it’s load.
Like the Electron dropping batteries halfway through the second stage burn, there is a mass multiplier. A ton of fuel dumped early means more than a ton of extra propellants for Centaur, enough to get to a stable orbit AND do a deorbit burn.
Are you thinking of something like the Shuttle using its OMS engines during ascent to (very slightly) increase its payload and/or orbital height?
-
#487
by
envy887
on 04 Jan, 2020 14:47
-
Sorry if I'm being confusing. The issue is whether a thrusters-out reentry is likely to succeed. You can be all lined up perfectly at entry interface--which is what will happen with a passive abort--but you still need some guidance to stay in the corridor in the atmosphere, because air makes guidance errors pile up a lot faster than vacuum does. If those errors result in going too steep or too shallow , there's a problem.
Bolded part is where I find your statements unclear. Specifically, I suspect you're worried about issues that can only materialize from much higher energy trajectories. Sent you a PM yesterday to try to get a better feel for where you envision the danger to be; would be perfectly happy to continue discussion there for the time being.
I find the tumbling issue mentioned by envy887 to be more concerning, although I take that article with a grain of salt since it doesn't go into much technical detail and some reporters tend to over-sensationalize.
FWIW, that article was written by Christian Davenport for the Washington Post. He generally knows what he's talking about in space articles, even if he does spice it up a little for general consumption.
-
#488
by
Comga
on 04 Jan, 2020 14:51
-
I have a serious question:
From the standpoint of the rocket equation, it is inefficient to bring modest Isp fuel, like that for the OMAC engines, using high Isp fuel like the LH2/LOX for Centaur.
Would it be possible to burn, say, a pair of 1,500 lb thrust OMAC engines to augment the 45,000 lb thrust RL-10 pair?
This could get rid of the unwanted fuel mass and save enough prop for the Centaur to do a deorbit burn. (and wind up with the same fuel margin as the reference mission)
Lockheed looked into using the LAS engine on Orion to augment the SLS. However, being solid launch abort engines, they could not be throttled, and the resulting massive thrust would have caused such a change in load paths that enormous structural redesign would have been required. In the end this idea was dropped.
But a pair of OMAC engines would be <7% of the thrust of the DEC, and the load on the Centaur would always remain positive, in compression.
The LAS engines are live, of course, before and during launch, but does this mean the OMAC engines are enabled or disabled? Do they fire during an abort for control or not?
The fuel becomes excess after MECO, where the LAS doesn’t have to start at a standstill, plow through the air at MaxQ, it outrun a nearly empty first stage. Before dropping the aeroskirt seems to be the perfect time to burn it thru the OMACs.
Just as with the escape tower idea, the rocket equation is not your friend. If OMACs are dragging around a half-full Centaur as well as the Starliner, the amount of delta-v they generate is pretty small, because the mass ratio is small.
No, it is my friend
It is precisely because it is NOT like the escape tower and the delta-V would be small that it could work.
The OMACs wouldn’t be “dragging” the Centaur as much as lightening it’s load.
Like the Electron dropping batteries halfway through the second stage burn, there is a mass multiplier. A ton of fuel dumped early means more than a ton of extra propellants for Centaur, enough to get to a stable orbit AND do a deorbit burn.
Are you thinking of something like the Shuttle using its OMS engines during ascent to (very slightly) increase its payload and/or orbital height?
Yes
Except that the OMS fuel was infinitesimal compared to the Orbiter but the OMAC fuel is a significant fraction. Not major but significant in the “hairy edge” nature of orbital vs suborbital.
-
#489
by
edkyle99
on 04 Jan, 2020 14:52
-
First 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
-
#490
by
Comga
on 04 Jan, 2020 14:57
-
Tumble = LOC
This has happened to a Russian cosmonaut.
Which one?
I thought Komarov’s Soyuz 1 parachute failure was caused by the capsule tumbling.
People here will correct me if that is wrong.
-
#491
by
ZachS09
on 04 Jan, 2020 15:08
-
Tumble = LOC
This has happened to a Russian cosmonaut.
Which one?
I thought Komarov’s Soyuz 1 parachute failure was caused by the capsule tumbling.
People here will correct me if that is wrong.
That is not true. The reason why the main parachute failed was because of some sort of defect in the deployment system, if I'm not mistaken. Komarov tried deploying the reserve chute, but it got tangled in the drogue chute and the capsule blew up upon the hard landing.
-
#492
by
Comga
on 04 Jan, 2020 15:38
-
Tumble = LOC
This has happened to a Russian cosmonaut.
Which one?
I thought Komarov’s Soyuz 1 parachute failure was caused by the capsule tumbling.
People here will correct me if that is wrong.
That is not true. The reason why the main parachute failed was because of some sort of defect in the deployment system, if I'm not mistaken. Komarov tried deploying the reserve chute, but it got tangled in the drogue chute and the capsule blew up upon the hard landing.
I stand corrected
People here are quite knowledgeable.
But I maintain, particularly during the hot part of reentry,
Tumble = LOC.
-
#493
by
clongton
on 04 Jan, 2020 19:13
-
Tumble = LOC
This has happened to a Russian cosmonaut.
Almost lost Gemini VIII in 1966 because of it. Tumbling caused pilot David Scott to black out and Neil Armstrong was on the very edge of it when he finally regained control. Another couple of seconds and they would have both died in a LOM/LOC mission failure.
-
#494
by
TheRadicalModerate
on 04 Jan, 2020 19:22
-
No, it is my friend
It is precisely because it is NOT like the escape tower and the delta-V would be small that it could work.
The OMACs wouldn’t be “dragging” the Centaur as much as lightening it’s load.
Like the Electron dropping batteries halfway through the second stage burn, there is a mass multiplier. A ton of fuel dumped early means more than a ton of extra propellants for Centaur, enough to get to a stable orbit AND do a deorbit burn.
OK, I happen to have a nasty spreadsheet that'll handle mixed-mode propulsion, so I configured a Centaur DEC and a Starliner to work in it. If we assume that we can burn 1.5 t of prop from 4 OMACs, each with a thrust of 1500 lbf and an Isp of 290 (can't find OMAC specs so Isp's a guess, based on an R-40B as the closest thing AJR has to an OMAC in their catalog), and overlap the burns so that they both end at Centaur MECO, then you get 321 m/s more delta-v at Centaur MECO than you would otherwise.
However, if you were to wait for Centaur MECO and jettison the Centaur before beginning the same OMAC burn, you'd get 349 m/s of delta-v.
So co-burning them costs you 28 m/s of delta-v. The rocket equation is not your friend.
-
#495
by
Comga
on 04 Jan, 2020 19:23
-
Tumble = LOC
This has happened to a Russian cosmonaut.
Almost lost Gemini VIII in 1966 because of it. Tumbling caused pilot David Scott to black out and Neil Armstrong was on the very edge of it when he finally regained control. Another couple of seconds and they would have both died in a LOM/LOC mission failure.
You almost got me to follow you down this rabbit hole.
(“But that wasn’t an aerodynamic tumble because blah blah blah...)
but the simple point remains undisputed:
Spacecraft tumbling during reentry, with forces well beyond the 100 lb thrust ACS engines, is not survivable.
What was described in the article would result in a Loss of Crew.
-
#496
by
TheRadicalModerate
on 04 Jan, 2020 19:23
-
Tumble = LOC
This has happened to a Russian cosmonaut.
Almost lost Gemini VIII in 1966 because of it. Tumbling caused pilot David Scott to black out and Neil Armstrong was on the very edge of it when he finally regained control. Another couple of seconds and they would have both died in a LOM/LOC mission failure.
Not quite on-point as an example, though. We've been talking about tumbling during reentry.
-
#497
by
JEF_300
on 04 Jan, 2020 20:54
-
Tumble = LOC
This has happened to a Russian cosmonaut.
Almost lost Gemini VIII in 1966 because of it. Tumbling caused pilot David Scott to black out and Neil Armstrong was on the very edge of it when he finally regained control. Another couple of seconds and they would have both died in a LOM/LOC mission failure.
You almost got me to follow you down this rabbit hole.
(“But that wasn’t an aerodynamic tumble because blah blah blah...)
but the simple point remains undisputed:
Spacecraft tumbling during reentry, with forces well beyond the 100 lb thrust ACS engines, is not survivable.
What was described in the article would result in a Loss of Crew.
Unless of course they were in a Soyuz, because as pointed out:
Perhaps he means Volynov. He experienced tumbling on reentry.
Yet he survived the reentry, albeit with broken teeth upon touchdown due to a soft-landing rocket malfunction.
Soyuz 5 was the specific mission. Could Starliner have survived what Soyuz 5 went through? My guess is probably not, but I think it's worth consideration.
On a tangental note, I've always wondered why we in the states don't design our reentry modules more like the way Soyuz was designed, with ablator all over. You can do a lot of things wrong on a Soyuz flight, but it'll come home as long as you can manage to drop the thing into the atmosphere, and that has to be an incredible comfort.
Although the multiple historical parachute failures and landing rockets mean you're probably only breaking even on comfort.
-
#498
by
clongton
on 04 Jan, 2020 21:03
-
You almost got me to follow you down this rabbit hole.
Not quite on-point as an example, though. We've been talking about tumbling during reentry.
Continued severe tumbling would likely have caused the death of both astronauts unless the Gemini ran out of thruster fuel first. In which case they would have eventually come around, only to be trapped in orbit. But in any case the spacecraft would eventually have reentered by itself and would still have been tumbling during reentry. If they hadn't actually died in orbit, the reentry would have killed them. That was the point I was making.
-
#499
by
TheRadicalModerate
on 04 Jan, 2020 21:08
-
First 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
You'll notice that that's merely the "performance" number for the N22 to an ISS orbit, not "Starliner performance". I suspect that that's on purpose.