Author Topic: SpaceX Dragon 2 Updates and Discussion - Thread 2  (Read 557226 times)

Online Joffan

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 2
« Reply #1280 on: 05/28/2018 06:41 PM »


That made NO sense.
The discussion centered on the availability of fuel, including how OATK can modify Cygnus to carry MORE fuel.
However, with NASA demanding that Dragon 2 lands under parachutes in the ocean the abort fuel is fully avaiilable for station reboost. After deorbit it itís probably more of a liability than a benefit. It would be better to burn it on orbit particularly with engines that face fully away from the ISS.
And the axial port is better for reboost as you said.
Abort fuel wouldn't be "fully" available. It would be used for regular orbital maneuvering if not used for abort. I don't know how much extra they might have.

There should be enough for propulsive landing (plus margin) and also orbital maneuvering (plus margin), since the nominal mission profile included both orbital maneuvering and propulsive landing.

Propulsive landing probably required over 500 m/s, and now that should be fully available on a nominal mission.

And in round numbers,  500m/s delta-v for a Dragon would translate into about 7 m/s delta-v for the ISS, and a 12km orbit raise. Not bad.
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Online speedevil

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 2
« Reply #1281 on: 05/28/2018 08:10 PM »
<snip 'how much margin'>
There should be enough for propulsive landing (plus margin) and also orbital maneuvering (plus margin), since the nominal mission profile included both orbital maneuvering and propulsive landing.

Propulsive landing probably required over 500 m/s, and now that should be fully available on a nominal mission.
In principle, given the experience with the platform, a lower delta-v rendevous could be done, with F9 dropping the dragon if not at the keep-out sphere, not far away.

Offline Comga

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 2
« Reply #1282 on: 05/28/2018 11:29 PM »


That made NO sense.
The discussion centered on the availability of fuel, including how OATK can modify Cygnus to carry MORE fuel.
However, with NASA demanding that Dragon 2 lands under parachutes in the ocean the abort fuel is fully avaiilable for station reboost. After deorbit it itís probably more of a liability than a benefit. It would be better to burn it on orbit particularly with engines that face fully away from the ISS.
And the axial port is better for reboost as you said.
Abort fuel wouldn't be "fully" available. It would be used for regular orbital maneuvering if not used for abort. I don't know how much extra they might have.

There should be enough for propulsive landing (plus margin) and also orbital maneuvering (plus margin), since the nominal mission profile included both orbital maneuvering and propulsive landing.

Propulsive landing probably required over 500 m/s, and now that should be fully available on a nominal mission.

And in round numbers,  500m/s delta-v for a Dragon would translate into about 7 m/s delta-v for the ISS, and a 12km orbit raise. Not bad.

We could estimate the delta V from the height of the arc of the ground abort.
Musk tweeted some numbers including 1187 m max altitude, 345 mph (units!) max velocity.
It may be a lot more than 500 m/s and therefore more than 12 km for the ISS.
Not only is this not bad, it's much more than the 0.06 m/s for the Cygnus test.
What kind of wastrels would dump a perfectly good booster in the ocean after just one use?

Offline jacqmans

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 2
« Reply #1283 on: 05/29/2018 02:25 PM »
NASA Astronaut Suni Williams, fully suited in SpaceXís spacesuit, interfaces with the display inside a mock-up of the Crew Dragon spacecraft in Hawthorne, California, during a testing exercise on Tuesday, April 3, 2018.

Photo credit: SpaceX

Offline jacqmans

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 2
« Reply #1284 on: 05/29/2018 02:25 PM »
NASA Astronaut Doug Hurley interfaces with the display inside a mock-up of the Crew Dragon spacecraft in Hawthorne, California, during a testing exercise on Tuesday, April 3, 2018.

Photo credit: SpaceX

Offline clongton

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 2
« Reply #1285 on: 05/29/2018 02:36 PM »
jacqmans, aren't the panels at eye level when dragon is rotated horizontal?
The photo appears as if she is looking (relative) up.
I'm wondering when the crew is in zero-g if they are looking straight ahead or looking up at the panels.
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Offline Coastal Ron

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 2
« Reply #1286 on: 05/29/2018 02:48 PM »
jacqmans, aren't the panels at eye level when dragon is rotated horizontal?
The photo appears as if she is looking (relative) up.
I'm wondering when the crew is in zero-g if they are looking straight ahead or looking up at the panels.

Astronaut Suni Williams appears to be using the interface panel in the way she would during the active part of a flight.

As I recall the panel can rotate away from her position when not in flight mode, which means the pivot point is between her position and what appears to be the top of the inside of the spacecraft.

If we don't continuously lower the cost to access space, how are we ever going to afford to expand humanity out into space?

Offline jpo234

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 2
« Reply #1287 on: 05/29/2018 02:54 PM »
jacqmans, aren't the panels at eye level when dragon is rotated horizontal?
The photo appears as if she is looking (relative) up.
I'm wondering when the crew is in zero-g if they are looking straight ahead or looking up at the panels.

During launch they will be in an eyes-in position, e.g. on their back. In this case it seems as if the panels will be directly above them (relative to the acceleration force). In zero g up and down kind of loses its meaning.

Edit: Add image with parallel lines showing backrest and panel orientation.
« Last Edit: 05/29/2018 04:11 PM by jpo234 »
You want to be inspired by things. You want to wake up in the morning and think the future is going to be great. That's what being a spacefaring civilization is all about. It's about believing in the future and believing the future will be better than the past. And I can't think of anything more exciting than being out there among the stars.

Offline Nomadd

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 2
« Reply #1288 on: 05/29/2018 03:43 PM »
 I couldn't sleep last night and watched Apollo 13 again. The panels have evolved a tiny bit since then.

http://www.darkroastedblend.com/2010/09/mega-dashboards-and-instrument-panels.html

http://digitalvideo.8m.net/D2Vcontrols1.jpg
« Last Edit: 05/30/2018 06:09 PM by Nomadd »

Offline deruch

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 2
« Reply #1289 on: 05/29/2018 11:40 PM »


That made NO sense.
The discussion centered on the availability of fuel, including how OATK can modify Cygnus to carry MORE fuel.
However, with NASA demanding that Dragon 2 lands under parachutes in the ocean the abort fuel is fully avaiilable for station reboost. After deorbit it itís probably more of a liability than a benefit. It would be better to burn it on orbit particularly with engines that face fully away from the ISS.
And the axial port is better for reboost as you said.
Abort fuel wouldn't be "fully" available. It would be used for regular orbital maneuvering if not used for abort. I don't know how much extra they might have.

There should be enough for propulsive landing (plus margin) and also orbital maneuvering (plus margin), since the nominal mission profile included both orbital maneuvering and propulsive landing.

Propulsive landing probably required over 500 m/s, and now that should be fully available on a nominal mission.

It could be also that the landing propellant would have provided the margin for the orbital maneuvering.  i.e. Significant contingency maneuvers on orbit would result in some form of a parachute landing--either propulsively assisted or straight into the water.  So bare minimum would be maneuvering + landing w/margin (OR maximum abort needs, whichever is greater). 

Sort of moot now though. :'(
Shouldn't reality posts be in "Advanced concepts"?  --Nomadd

Offline Nomadd

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 2
« Reply #1290 on: 05/30/2018 07:47 PM »
 It seems like handling a chute failure scenario would be no more than a little software if you had the fuel. What reason could there possibly be for not using an available means to slow down if you're headed for a terminal (pun intended) velocity impact?
« Last Edit: 05/30/2018 07:48 PM by Nomadd »

Offline Comga

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 2
« Reply #1291 on: 05/30/2018 07:55 PM »
It seems like handling a chute failure scenario would be no more than a little software if you had the fuel. What reason could there possibly be for not using an available means to slow down if you're headed for a terminal (pun intended) velocity impact?

Propulsive landing as a backup to the redundant parachutes?
That's quite a stretch.

One advantage Cygnus has over Dragon 2 for reboost is that it is also pointed very near the CG when berthed to Node 1 Nadir, but the station only has to pitch ~90 degrees to point the engine forward.
If Dragon 2 were to be used for reboost when docked to Node 2 Forward the station would have to yaw or pitch through about 180 degrees.
What kind of wastrels would dump a perfectly good booster in the ocean after just one use?

Offline Nomadd

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 2
« Reply #1292 on: 05/30/2018 08:04 PM »
It seems like handling a chute failure scenario would be no more than a little software if you had the fuel. What reason could there possibly be for not using an available means to slow down if you're headed for a terminal (pun intended) velocity impact?

Propulsive landing as a backup to the redundant parachutes?
That's quite a stretch. .
Why? You have the engines. All you'd have to do is fire them. We're not talking about adding legs or anything.
 If they'd added a few simple commands in the early days, they might have saved the CRS-7 capsule and payload.
« Last Edit: 05/30/2018 08:05 PM by Nomadd »

Offline clongton

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 2
« Reply #1293 on: 05/30/2018 08:22 PM »
Propulsive landing as a backup to the redundant parachutes?
That's quite a stretch.
Why? You have the engines. All you'd have to do is fire them. We're not talking about adding legs or anything.
 If they'd added a few simple commands in the early days, they might have saved the CRS-7 capsule and payload.

In My Opinion: SpaceX should maintain the option of propulsive landing - on the heatshield. They deleted the landing legs so there is no more option for "landing like a spaceship is supposed to land". But if there is an emergency abort and they just have to get down now and there is no ocean to target, they will hit wherever they hit. If there is also a parachute failure that is going to be an awfully hard hit - unless they can fire the SDs to slow the impact. So yes: "Propulsive landing as a backup to the redundant parachutes".  It's a perfect backup system. Just because they can doesn't mean they normally will. They will normally parachute to an intended location on the ocean, but for the contingencies? Yes, propulsive landing on the heatshield.
« Last Edit: 05/30/2018 08:25 PM by clongton »
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Offline Comga

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 2
« Reply #1294 on: 05/31/2018 03:40 AM »
It seems like handling a chute failure scenario would be no more than a little software if you had the fuel. What reason could there possibly be for not using an available means to slow down if you're headed for a terminal (pun intended) velocity impact?

Propulsive landing as a backup to the redundant parachutes?
That's quite a stretch. .
Why? You have the engines. All you'd have to do is fire them. We're not talking about adding legs or anything.
 If they'd added a few simple commands in the early days, they might have saved the CRS-7 capsule and payload.

What Musk said was if the Dragon on CRS-7 could have released the parachutes, it would have landed safely in the ocean.
But popping chutes is inherently simpler than a propulsive landing.
Once it goes through the drogues and unreefing, it’s stable until it hits the water.
Powered descent isn’t stable.
(I have been tryin to guess how the Dragon would sense the altitude with enough precision to slow to a stop at zero altitude. Where would they mount a radar?   Could they use a vision system looking out the window?)

On the other hand I volunteer to be the (overaged) intern who gets fired for disabling the chutes that forces the Dragon to do a propulsive landing as “a backup”.
« Last Edit: 05/31/2018 03:43 AM by Comga »
What kind of wastrels would dump a perfectly good booster in the ocean after just one use?

Offline CameronD

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 2
« Reply #1295 on: 05/31/2018 04:07 AM »
(I have been tryin to guess how the Dragon would sense the altitude with enough precision to slow to a stop at zero altitude. Where would they mount a radar?   Could they use a vision system looking out the window?)

A radar altimeter seems the obvious solution and presumably they already need one to jettison parachutes after touchdown?

https://buy.garmin.com/en-US/US/p/166298

The radomes are comparatively tiny and with some tweaking of frequencies could possibly be mounted between the heat-shield and the shell..

« Last Edit: 05/31/2018 04:09 AM by CameronD »
With sufficient thrust, pigs fly just fine - however, this is not necessarily a good idea. It is hard to be sure where they are
going to land, and it could be dangerous sitting under them as they fly overhead.

Offline biosehnsucht

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 2
« Reply #1296 on: 05/31/2018 05:27 AM »
Radar works for Falcon 9 first stage ... so as long as you can find a place to put it, that's one less show stopper.

Offline deruch

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 2
« Reply #1297 on: 05/31/2018 06:29 AM »
The problem is the field of view and angle to the water.  The hypothetical situation this is being discussed for requires at least 2 parachutes of 4 to fail (they already have enough "drag margin" to land safely under 3).  In which case, there's not much guarantee for the attitude of the capsule as it is coming down.  So, now to enable this mode they have to be able to accurately measure the altitude even when the capsule is in off nominal attitudes.  That's a harder challenge.
Shouldn't reality posts be in "Advanced concepts"?  --Nomadd

Offline Johnnyhinbos

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 2
« Reply #1298 on: 05/31/2018 10:39 AM »
Iíll just mention this one last time...

So for everyone voicing the opinion that propulsive landing on the heatshield in an extreme emergency should be preserved:

Youíre saying you think NASA and ASAP will be fine carrying enough extremely volitile hypergolic fuel aboard a capsule carrying humans - enough to light four extremely thirsty super Dracoís to slow the D2 from freefall to standstill - in the event of a third level failure. Which would be saying that they see the probability of likelihood of this failure mode high enough to merit this level of risk. And by you thinking they WOULD think this, then by extension you are saying the same should therefore apply to their own Orion capsule, which also comes down under chutes and therefore has the same criteria for failure.

If you believe all that, then I guess youíre expecting them now have to design an emergency propulsive lander for Orion. Sure - whatís another decade of program delay...
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Offline DistantTemple

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 2
« Reply #1299 on: 05/31/2018 12:00 PM »
Developing thoughts:
Your logic that the increased risk of extra propellant should be balanced against the decreased (3rd level) risk afforded by an emergency propulsive landing, makes sense.

Quote from: Johnnyhinbos
carrying enough extremely volitile hypergolic fuel aboard a capsule carrying humans - enough to light four extremely thirsty super Dracoís to slow the D2 from freefall to standstill -

However you have emotively and implicitly claimed that there is a (significantly) greater risk, from this change/increase.

Despite the discussion above I don't think we know even approximately the volumes, energy, or even fractional difference in the two propellant scenarios. And so apart from empty/almost empty tanks, we cannot evaluate whether a change from say 1/4 full to 3/4 full would make a difference or whether both are equally a LODragon/LOC event or not, in any possible accident scenario.

... well I have now talked myself into partial agreement with you. One risk from such extra propellant (say 3 times as much for a guess) is from external impact during crew egress, or loading onto the recovery ship, because of rough sea or handling accident. (this extends until all propellant is removed). Then the additional risk could be critical, and fatal. However precautions must already be in place to mange this. .... but I see no other place where more or less propellant  would change risk to the dragon or crew on entry descent or landing. ... And bursting into flames on a hard impact, would be avoided by the propulsive landing! ... Hypothetically I suppose after an unplanned emergency reentry, where the Dragon descends over land, with buildings, or mountains, then any residual propellant could be a significant problem!

We assume the tanks are completely full for launch escape on all missions. We discuss if more can be deliberately used than needed to reduce the load for safety reasons, but that would complicate the mission profile, adding risk. Boosting the SS is conjecture. I believe the fuel cannot be dumped, only burned in the engines, so there is no procedure for reducing fuel. Therefore IMO your point and mine end up being moot.
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