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#620
by
AS-503
on 02 Mar, 2017 09:36
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There is no way a human pilot can "steer" a manned space craft manually through re-entry (limiting g loads, structural loads, thermal loads). If the systems are not able to do it automatically how can these "offline" systems give the pilot the critical data he/she would need for this already impossible task? There is no stick-and-rudder approach to re-entry.
Somewhere, Gordon Cooper is laughing his [posterior] off at that ... 
The context here is re-entry from BEO. Does the laughing still apply?
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#621
by
guckyfan
on 02 Mar, 2017 09:40
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The key point seems to be to me at least. There are no longer wires going from a switch to an engine. The whole thing is hooked up to a computer. As long as the computer works, a human has nothing to do. When it does not work, there is nothing a human can do.
Except I remember from the early days that entry is passively stable. So once you are on a survivable reentry path you can do with complete computer failure. The parachutes can be manually activated in that situation.
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#622
by
AS-503
on 02 Mar, 2017 10:11
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The key point seems to be to me at least. There are no longer wires going from a switch to an engine. The whole thing is hooked up to a computer. As long as the computer works, a human has nothing to do. When it does not work, there is nothing a human can do.
Except I remember from the early days that entry is passively stable. So once you are on a survivable reentry path you can do with complete computer failure. The parachutes can be manually activated in that situation.
Your statement says "once your one a survivable path", at what point in a BEO reentry with computer failure are you on a survivable path?
If you watch the NASA Apollo era video that was posted on page 8 (reply 158) of this thread, you will see how the BEO reentry is controlled by the computer. Small-ish errors in the reentry corridor angle which may or may not be discernible by a human pilot with no computer will most likely result in excessive g/structural/thermal loads (too steep) or skipping off the atmosphere (too shallow). Also the steering (pitch/yaw/roll) done by the computer provides the necessary/correct cross-range for landing accuracy. The human pilot could not carry that task out with a high level of reliability.
Personally I am very excited for this crewed proposal, but I will not argue for the case of having the humans in the loop to provide BEO reentry back up. Its kind of like that argument about having the Falcon 9 landing being dynamically controlled with feedback from the ASDS in real-time vs. the autonomous way it is actually done.
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#623
by
guckyfan
on 02 Mar, 2017 10:23
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Your statement says "once your one a survivable path", at what point in a BEO reentry with computer failure are you on a survivable path?
If you watch the NASA Apollo era video that was posted on page 8 (reply 158) of this thread, you will see how the BEO reentry is controlled by the computer.
With Apollo 13 they were able to hit the reentry corridor manually. The point I was trying to make is, this is no longer possible with the electronics controlling everything. There is no point in having a pilot.
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#624
by
TaurusLittrow
on 02 Mar, 2017 10:24
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There is no way a human pilot can "steer" a manned space craft manually through re-entry (limiting g loads, structural loads, thermal loads). If the systems are not able to do it automatically how can these "offline" systems give the pilot the critical data he/she would need for this already impossible task? There is no stick-and-rudder approach to re-entry.
Somewhere, Gordon Cooper is laughing his [posterior] off at that ...
Well, I think the center of gravity of Mercury was the same as the geometric center so it would not have been possible to alter the trajectory by rolling the spacecraft. Gordo flipped switches in the right order when the automatic sequencer went down before entry. However, I do recall Mike Collins writing that he was prepared to take manual control over the roll sequence of the CM if the computer malfunctioned on entry on Apollo 11.
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#625
by
Ben the Space Brit
on 02 Mar, 2017 10:38
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One significant difference between Apollo and Dragon Mk2 is that the Apollo autopilot and flight control systems, although linked, went through different systems. The manual flight controls would operate even in the event of a navigation computer failure.
I'm not so sure that Dragon's flight controls would work in the event that the GNC system went down. From what I saw of the roll-out presser, Dragon Mk2 looks a lot more glass-and-software with very few physical controls. I mean, I'd like to assume that GNC and flight control are on separate, redundant circuits that talk but are not one and the same (so that one dying doesn't kill the other) but I don't know that for certain.
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#626
by
Lee Jay
on 02 Mar, 2017 11:58
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I've been sick and out-of-the-loop the last couple of days, but reading this made me a bit depressed.
So I went back and started reading the thread from the beginning.
Looks like I'm not the only one, but pretty darned close.
The more I see of this sort of thing the more disenfranchised I feel about where spaceflight is actually heading versus where I'd like it to be heading.
Sure, I'll watch the mission carefully, and even be excited doing so (I'm a techno-geek), but this sort of thing - and SpaceX's Mars plans in general - are not where I'd like us to be going in spaceflight, especially human spaceflight.
In a way, I completely agree, and then in another way, disagree....
If there was no context to this, and all you'd be telling me is about a company that built the minimal infrastructure required to fly around the moon, for tourism purposes, I'd be with you - puke. Neil Armstrong, for this?!
But there is context. This is a company focused on the real thing - beyond exploration even - actually forming a spacefaring civilization. Sacred words, pretty much, straight out of childhood's sci-fi.
I don't like their Mars plans either. They're focued on colinization which is folly and about the fifteenth major step in a human Mars program. We're on about step three.
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#627
by
rsdavis9
on 02 Mar, 2017 12:01
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Wow. I can't remember hearing so much whining in a thread in a long time in NSF. Two people are going to PAY SpaceX for a trip around the Moon!
"Waah! It's shouldn't be rich people! It should be someone from Category X that I like better and paid for by someone else!" "Waah! They can't do it without a professional astronaut!" Waah! They're just tourists!" "Waah! It's too dangerous! Let's sneer at it and maybe it'll go away!"
I wonder if the same thing happened on, say, oceanographic forums condemning Cameron for going to the bottom of the Marianas Trench as a TOURIST? Probably did, if the same kind of people are on there. Or let's pile on anyone who pays a bunch of money to jump out of a balloon in the Stratosphere: "Waah! That should only be done by professional test pilots!".
What is the matter here? It's their money, not yours. Someone is helping push BEO flight along and some of you are acting like they are killing babies or something.
I'd go in a heartbeat. Crowdfunding, anybody?
I'm thinking crowd funding of some creative sort is maybe how elon gets his 10b to build ITS. Not sure what it is yet but crowd funding does amazing things these days.
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#628
by
Mongo62
on 02 Mar, 2017 12:18
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But the existing mounting hardware is a show-stopper. Designing and fabricating a one-off set of mounting hardware to hold the Cargo Dragon for just this flight would be too expensive. Unless... can an additional adapter to fit the Cargo Dragon trunk to the existing Falcon Heavy mounting hardware be fabricated and tested
Sorry, you've lost me. Excuse my ignorance, but isn't FH S2 basically a F9 S2? Why is it different to mount a Dragon on a FH compared to what SpaceX already does with the F9?
The second stage itself is basically the same, as far as I know, but when a fairing is used, as is required for the test flight by the Air Force, the Dragon can no longer be mounted directly to the second stage. There is mounting hardware inside the fairing, which has a smaller diameter than the second stage, and does not fit the Dragon's mounting points (which is designed to fit the second stage).
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#629
by
rsdavis9
on 02 Mar, 2017 12:19
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People forget that elon started with a russian rocket to put a greenhouse with plants on mars. If that isn't frivolous what is? He is a master presenter of ideas to the public. People around the moon is just another master idea to ignite interest in the public.
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#630
by
ugordan
on 02 Mar, 2017 12:53
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The second stage itself is basically the same, as far as I know, but when a fairing is used, as is required for the test flight by the Air Force, the Dragon can no longer be mounted directly to the second stage.
Is this a statement of fact or an assumption?
I do agree with your point that trying to fly a Dragon on the inaugural FH flight would go against qualifying the fairing for the (likely higher) max Q environment than on a single stick F9, which would kind of defeat the purpose of the demo flight when it comes to USAF. I guess it boils down to what kind of risk USAF would be willing to take. I personally don't see Dragon on FH-01 happening, but I've been proven wrong before.
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#631
by
cscott
on 02 Mar, 2017 13:42
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I do not remember seeing any definitive statement that a fairing was required on the falcon heavy demo flight. Lots of NSFers making assumptions, but no actual facts.
And the NSFers were making their points to argue that dragon wouldn't be on top of the falcon heavy demo flight. This news from Elon strongly implies the opposite.
I'm not saying who was right and wrong, but I wouldn't treat either option as gospel yet. Unless someone can dig up an authoritative source.
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#632
by
mme
on 02 Mar, 2017 13:57
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...
What is the matter here? It's their money, not yours. Someone is helping push BEO flight along and some of you are acting like they are killing babies or something.
I'd go in a heartbeat. Crowdfunding, anybody?
Just remember this: Space tourist dispute deepens
NASA threw a tantrum when Dennis Tito flew to the ISS.
I think that has more to do with the effects of the tourist on the safety and operation of the ISS and any extra burdens for NASA than the concept of space tourists in general. NASA may or may not be a fan of the private cislunar (circumlunar?) mission but it's not effecting NASA operations or astronauts.
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#633
by
mme
on 02 Mar, 2017 14:13
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But the existing mounting hardware is a show-stopper. Designing and fabricating a one-off set of mounting hardware to hold the Cargo Dragon for just this flight would be too expensive. Unless... can an additional adapter to fit the Cargo Dragon trunk to the existing Falcon Heavy mounting hardware be fabricated and tested
Sorry, you've lost me. Excuse my ignorance, but isn't FH S2 basically a F9 S2? Why is it different to mount a Dragon on a FH compared to what SpaceX already does with the F9?
The second stage itself is basically the same, as far as I know, but when a fairing is used, as is required for the test flight by the Air Force, the Dragon can no longer be mounted directly to the second stage. There is mounting hardware inside the fairing, which has a smaller diameter than the second stage, and does not fit the Dragon's mounting points (which is designed to fit the second stage).
I think the solution to the problem is to just accept that Dragon launches don't count toward AF acceptance. I doubt using a custom PF would count anyway and it seems like just asking for trouble IMO.
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#634
by
ugordan
on 02 Mar, 2017 14:17
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I think the solution to the problem is to just accept that Dragon launches don't count toward AF acceptance.
That's not really a "solution" for the topic of this thread if you consider the limited number of flights FH can realistically have by the time the end-of-2018 timeframe comes. People didn't start invoking Dragon on the FH demo for no particular reason, but as a means to make that schedule
somewhat more realistic.
Some things to consider:
1. FH won't fly from 39A until 40 is back in action.
2. 40 repairs were basically on hold until 39A became operational.
3. because of 2. IMHO it's very optimistic to expect 40 to be rebuilt by even late summer.
4. Despite many past claims on production rate of vehicles, it's still obvious that production is lagging and the only way they can get several flight cores in the launch pipeline is if Something Bad happens and there's a launch campaign standdown. Case in point - Iridium at VAFB.
5. Each FH requires 3 first stage acceptance campaigns at McGregor, which will inevitably have to compete with single cores for their non-shrinking manifest.
All of this combined suggests the number of FHs launched in the next 2 years will be low, even if we assume no major snags during the inaugural campaign. This leaves very few opportunities to test a Dragon 2 with a BEO-like reentry velocity. As for the recent comments about increased production rate later this year, we've heard it all before. Seeing is believing.
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#635
by
douglas100
on 02 Mar, 2017 14:22
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One significant difference between Apollo and Dragon Mk2 is that the Apollo autopilot and flight control systems, although linked, went through different systems. The manual flight controls would operate even in the event of a navigation computer failure.
I'm not so sure that Dragon's flight controls would work in the event that the GNC system went down. From what I saw of the roll-out presser, Dragon Mk2 looks a lot more glass-and-software with very few physical controls. I mean, I'd like to assume that GNC and flight control are on separate, redundant circuits that talk but are not one and the same (so that one dying doesn't kill the other) but I don't know that for certain.
The important thing is that the computers don't go down. Without them you don't get home. There are
no manual controls on Dragon unlike Mercury.
All control inputs go though computers.
There are a few other critical systems for navigation, particularly star trackers and the IMU, (also, of course, communications.) The technology for these things has come on a lot since Apollo. And you would expect a lot of redundancy in these systems.
There is
nothing for the crew to do on this flight as far as navigation is concerned. The spacecraft can do a lot of it autonomously along with ground command. The crew might have the option of choosing the attitude to get a better view during the flight, but that would have nothing to do with navigation.
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#636
by
envy887
on 02 Mar, 2017 14:34
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I think the solution to the problem is to just accept that Dragon launches don't count toward AF acceptance.
That's not really a "solution" for the topic of this thread if you consider the limited number of flights FH can realistically have by the time the end-of-2018 timeframe comes. People didn't start invoking Dragon on the FH demo for no particular reason, but as a means to make that schedule somewhat more realistic.
Some things to consider:
1. FH won't fly from 39A until 40 is back in action.
2. 40 repairs were basically on hold until 39A became operational.
3. because of 2. IMHO it's very optimistic to expect 40 to be rebuilt by even late summer.
4. Despite many past claims on production rate of vehicles, it's still obvious that production is lagging and the only way they can get several flight cores in the launch pipeline is if Something Bad happens and there's a launch campaign standdown. Case in point - Iridium at VAFB.
5. Each FH requires 3 first stage acceptance campaigns at McGregor, which will inevitably have to compete with single cores for their non-shrinking manifest.
All of this combined suggests the number of FHs launched in the next 2 years will be low, even if we assume no major snags during the inaugural campaign. This leaves very few opportunities to test a Dragon 2 with a BEO-like reentry velocity. As for the recent comments about increased production rate later this year, we've heard it all before. Seeing is believing.
Falcon 9 Block 5 can almost certainly launch Dragon 2 around the Moon if it doesn't need to carry any payload and they are willing to throw the booster away. No need for FH for Dragon test flights.
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#637
by
ugordan
on 02 Mar, 2017 14:43
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Falcon 9 Block 5 can almost certainly launch Dragon 2 around the Moon if it doesn't need to carry any payload and they are willing to throw the booster away. No need for FH for Dragon test flights.
You're making this statement based on what numbers? What is implied by no payload? An empty shell with nothing but RCS and comms? Does launching a boilerplate shell make an accurate test of TPS and reentry performance as the energy to dissipate per surface area goes up linearly with mass, E=(mv*v)/2?
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#638
by
envy887
on 02 Mar, 2017 15:00
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Falcon 9 Block 5 can almost certainly launch Dragon 2 around the Moon if it doesn't need to carry any payload and they are willing to throw the booster away. No need for FH for Dragon test flights.
You're making this statement based on what numbers? What is implied by no payload? An empty shell with nothing but RCS and comms? Does launching a boilerplate shell make an accurate test of TPS and reentry performance as the energy to dissipate per surface area goes up linearly with mass, E=(mv*v)/2?
Advertised payload to GTO of 8,300 kg (presumably GTO-1800). That corresponds to 6,850 kg to TLI, which is right around where a dry Dragon 2 is estimated. Certainly more than a boilerplate.
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#639
by
rakaydos
on 02 Mar, 2017 15:02
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I've been sick and out-of-the-loop the last couple of days, but reading this made me a bit depressed.
So I went back and started reading the thread from the beginning.
Looks like I'm not the only one, but pretty darned close.
The more I see of this sort of thing the more disenfranchised I feel about where spaceflight is actually heading versus where I'd like it to be heading.
Sure, I'll watch the mission carefully, and even be excited doing so (I'm a techno-geek), but this sort of thing - and SpaceX's Mars plans in general - are not where I'd like us to be going in spaceflight, especially human spaceflight.
In a way, I completely agree, and then in another way, disagree....
If there was no context to this, and all you'd be telling me is about a company that built the minimal infrastructure required to fly around the moon, for tourism purposes, I'd be with you - puke. Neil Armstrong, for this?!
But there is context. This is a company focused on the real thing - beyond exploration even - actually forming a spacefaring civilization. Sacred words, pretty much, straight out of childhood's sci-fi.
I don't like their Mars plans either. They're focued on colinization which is folly and about the fifteenth major step in a human Mars program. We're on about step three.
You think he hasnt thought about steps four through fourteen?
