Author Topic: SpaceX Dragon 2 Updates and Discussion - Thread 2  (Read 220988 times)

Offline Jim

  • Night Gator
  • Senior Member
  • *****
  • Posts: 31292
  • Cape Canaveral Spaceport
  • Liked: 9570
  • Likes Given: 299
Re: SpaceX Dragon 2 Updates and Discussion - Thread 2
« Reply #420 on: 07/17/2017 07:59 PM »

I would think it could get to ISS fast without the ISS having to maneuver.. would also use up some of those nasty hypergols.

Launch provides the fast ascent and not so much maneuvering propellant.

Online dror

  • Full Member
  • ****
  • Posts: 550
  • Israel
  • Liked: 122
  • Likes Given: 346
Re: SpaceX Dragon 2 Updates and Discussion - Thread 2
« Reply #421 on: 07/17/2017 08:26 PM »
My expectation is NASA will have SpaceX burn off the hypergol fuel before re-entry. It will be another event (like removing an LAS tower), but would be less risky then landing with the fuel as you say.

What's the best use of the fuel if not for landings? Can they decelerate enough to take stress off the heat shield?
Or should they reboost ISS before undocking? Can D2 do reboosts?
This may be a silli question,
Can it be designed to transfer the access fuel to the ISS?
I mean, apart from the effect on the Dragon's CoG
"If we crave some cosmic purpose, then let us find ourselves a worthy goal. "
Carl Sagan, Pale Blue Dot

Offline starsilk

  • Full Member
  • ****
  • Posts: 622
  • Denver
  • Liked: 212
  • Likes Given: 40
Re: SpaceX Dragon 2 Updates and Discussion - Thread 2
« Reply #422 on: 07/17/2017 08:46 PM »

I would think it could get to ISS fast without the ISS having to maneuver.. would also use up some of those nasty hypergols.

Launch provides the fast ascent and not so much maneuvering propellant.

seems like plentiful maneuvering propellant should make it possible to overcome an uncooperative target.

Online tater

  • Member
  • Posts: 23
  • NM
  • Liked: 5
  • Likes Given: 41
Re: SpaceX Dragon 2 Updates and Discussion - Thread 2
« Reply #423 on: 07/17/2017 09:08 PM »
I think I would have the crew spacecraft monitor parachute deployment, and if there were to be an unsurvivable parachute failure, then it propulsively lands in the ocean. The best use would be to protect the crew if at all possible, no?

(obviously it would have to be programmed for that as a possible contingency)

Offline Jim

  • Night Gator
  • Senior Member
  • *****
  • Posts: 31292
  • Cape Canaveral Spaceport
  • Liked: 9570
  • Likes Given: 299
Re: SpaceX Dragon 2 Updates and Discussion - Thread 2
« Reply #424 on: 07/18/2017 01:34 AM »
My expectation is NASA will have SpaceX burn off the hypergol fuel before re-entry. It will be another event (like removing an LAS tower), but would be less risky then landing with the fuel as you say.

What's the best use of the fuel if not for landings? Can they decelerate enough to take stress off the heat shield?
Or should they reboost ISS before undocking? Can D2 do reboosts?
This may be a silli question,
Can it be designed to transfer the access fuel to the ISS?
I mean, apart from the effect on the Dragon's CoG


no, it would have to dock to the russian segment for that

Offline Jim

  • Night Gator
  • Senior Member
  • *****
  • Posts: 31292
  • Cape Canaveral Spaceport
  • Liked: 9570
  • Likes Given: 299
Re: SpaceX Dragon 2 Updates and Discussion - Thread 2
« Reply #425 on: 07/18/2017 01:36 AM »

seems like plentiful maneuvering propellant should make it possible to overcome an uncooperative target.

It has nothing to do with uncooperative target.  And there is a limit to what propellant can do. 
Like I said, fast ascent is a launch targeting issue and not maneuvering propellant

Offline Norm38

  • Full Member
  • ****
  • Posts: 991
  • Liked: 382
  • Likes Given: 509
Re: SpaceX Dragon 2 Updates and Discussion - Thread 2
« Reply #426 on: 07/18/2017 01:56 AM »
Jim,
It was mentioned earlier that ISS itself has to maneuver to support a fast rendezvous. Is that not true? If it is, isn't it more efficient for the smaller visiting vehicle to maneuver than the ISS?

Offline starsilk

  • Full Member
  • ****
  • Posts: 622
  • Denver
  • Liked: 212
  • Likes Given: 40
Re: SpaceX Dragon 2 Updates and Discussion - Thread 2
« Reply #427 on: 07/18/2017 04:09 AM »

seems like plentiful maneuvering propellant should make it possible to overcome an uncooperative target.

It has nothing to do with uncooperative target.  And there is a limit to what propellant can do. 
Like I said, fast ascent is a launch targeting issue and not maneuvering propellant
Uncooperative = political games.

There's a limit to what propellant can do? That's an odd statement. A lot of propellant can do all sorts of things in orbit... And dragon 2 will have a LOT to burn off.

Offline Comga

  • Senior Member
  • *****
  • Posts: 3911
  • Liked: 1232
  • Likes Given: 1050
Re: SpaceX Dragon 2 Updates and Discussion - Thread 2
« Reply #428 on: 07/18/2017 05:41 AM »
A question I could answer myself if I had enough time to program the equations:
If a Dragon in a circular orbit about the altitude of the ISS used all of its maneuvering fuel to enter an elliptical orbit, by how much could it increase its orbital period?  What's the max delta-V?
In reverse, this is the maximum phasing per orbit that could be utilized by a Dragon boosted by the second stage into an orbit with an apogee above the ISS. (Which is limited by the rocket performance.  Not sure how that would be calculated.)
This would be an inverted version of a normal launch to the ISS where the arriving ship "catches up" from below and behind" only it wouldn't be limited by the atmosphere.
What kind of wastrels would dump a perfectly good booster in the ocean after just one use?

Offline soltasto

Re: SpaceX Dragon 2 Updates and Discussion - Thread 2
« Reply #429 on: 07/18/2017 09:32 AM »
My expectation is NASA will have SpaceX burn off the hypergol fuel before re-entry. It will be another event (like removing an LAS tower), but would be less risky then landing with the fuel as you say.

What's the best use of the fuel if not for landings? Can they decelerate enough to take stress off the heat shield?
Or should they reboost ISS before undocking? Can D2 do reboosts?
This may be a silli question,
Can it be designed to transfer the access fuel to the ISS?
I mean, apart from the effect on the Dragon's CoG


no, it would have to dock to the russian segment for that

I theory a revision to the International docking standard and a subsequent upgrade to the ISS US segment docking adapters could allow for water, fuel, oxidizer and pressurant transfer.

This kind of transfer is currently "reserved" from sections 3.4.2 to 3.4.5 in the official document attached below

International Docking System Standard
(IDSS)
Interface Definition Document (IDD)
Revision E

Offline Jim

  • Night Gator
  • Senior Member
  • *****
  • Posts: 31292
  • Cape Canaveral Spaceport
  • Liked: 9570
  • Likes Given: 299
Re: SpaceX Dragon 2 Updates and Discussion - Thread 2
« Reply #430 on: 07/18/2017 02:37 PM »

There's a limit to what propellant can do? That's an odd statement. A lot of propellant can do all sorts of things in orbit... And dragon 2 will have a LOT to burn off.

 Not really "a lot" in the true scheme of thing. 

Not when the spacecraft has limited orbital life. 


Uncooperative = political games.


And wrong about that.  ISS maneuvering means more propellant has to be brought up.
« Last Edit: 07/18/2017 02:47 PM by Jim »

Offline Jim

  • Night Gator
  • Senior Member
  • *****
  • Posts: 31292
  • Cape Canaveral Spaceport
  • Liked: 9570
  • Likes Given: 299
Re: SpaceX Dragon 2 Updates and Discussion - Thread 2
« Reply #431 on: 07/18/2017 02:39 PM »
revision to the International docking standard and a subsequent upgrade to the ISS US segment docking adapters could allow for water, fuel, oxidizer and pressurant transfer.


Not feasible to plumb the ISS US segment for el, oxidizer and pressurant transfer.  It would still have to go to the Russian segment.

Offline Jim

  • Night Gator
  • Senior Member
  • *****
  • Posts: 31292
  • Cape Canaveral Spaceport
  • Liked: 9570
  • Likes Given: 299
Re: SpaceX Dragon 2 Updates and Discussion - Thread 2
« Reply #432 on: 07/18/2017 02:49 PM »
Jeesh, doe this have to be explained again.  The two day transfer to the ISS allows for daily launch windows.  The fast transfer does not and the amount of spacecraft propellant has limited affect on this.

Offline starsilk

  • Full Member
  • ****
  • Posts: 622
  • Denver
  • Liked: 212
  • Likes Given: 40
Re: SpaceX Dragon 2 Updates and Discussion - Thread 2
« Reply #433 on: 07/18/2017 03:35 PM »

There's a limit to what propellant can do? That's an odd statement. A lot of propellant can do all sorts of things in orbit... And dragon 2 will have a LOT to burn off.

 Not really "a lot" in the true scheme of thing. 

random internet speculators out there say 400-450 m/s. that seems like a lot.


Not when the spacecraft has limited orbital life. 

superdracos can apply all of that in < 10 seconds. not that they would want to, but there will be more than enough capability to apply the delta-v quickly.


Uncooperative = political games.


And wrong about that.  ISS maneuvering means more propellant has to be brought up.

which means money needs to be paid for fuel supply. which means political games.

far, far simpler for the spacecraft to do it than the space station.

ah well, instead they can take all that dangerous fuel to the ISS for 6 months. then do the world's largest re-entry burn instead.

Online JasonAW3

  • Senior Member
  • *****
  • Posts: 2418
  • Claremore, Ok.
  • Liked: 377
  • Likes Given: 10
Re: SpaceX Dragon 2 Updates and Discussion - Thread 2
« Reply #434 on: 07/18/2017 03:49 PM »
revision to the International docking standard and a subsequent upgrade to the ISS US segment docking adapters could allow for water, fuel, oxidizer and pressurant transfer.


Not feasible to plumb the ISS US segment for el, oxidizer and pressurant transfer.  It would still have to go to the Russian segment.

Jim, wasn't there some discussion about an interim propulsion module a couple of years back, when Russia was considering pulling their segment of the ISS out to form their own space station complex?
My God!  It's full of universes!

Online Lars-J

  • Senior Member
  • *****
  • Posts: 3455
  • California
  • Liked: 2691
  • Likes Given: 1702
Re: SpaceX Dragon 2 Updates and Discussion - Thread 2
« Reply #435 on: 07/18/2017 04:26 PM »
revision to the International docking standard and a subsequent upgrade to the ISS US segment docking adapters could allow for water, fuel, oxidizer and pressurant transfer.


Not feasible to plumb the ISS US segment for el, oxidizer and pressurant transfer.  It would still have to go to the Russian segment.

Jim, wasn't there some discussion about an interim propulsion module a couple of years back, when Russia was considering pulling their segment of the ISS out to form their own space station complex?

There were several variants proposed: https://en.wikipedia.org/wiki/ISS_Propulsion_Module

But none of them would use propellant transfer. It would have been an expendable stop gap module, and it was more of a back-up plan if Zvezda failed to launch.

Offline Jim

  • Night Gator
  • Senior Member
  • *****
  • Posts: 31292
  • Cape Canaveral Spaceport
  • Liked: 9570
  • Likes Given: 299
Re: SpaceX Dragon 2 Updates and Discussion - Thread 2
« Reply #436 on: 07/18/2017 04:35 PM »

random internet speculators out there say 400-450 m/s. that seems like a lot.

superdracos can apply all of that in < 10 seconds. not that they would want to, but there will be more than enough capability to apply the delta-v quickly.


Neither are going to make rendezvous quicker.

If the Dragon is not launched at the proper time, it will take many more days for it to catch up with the ISS. 

2 day rendezvous provides for launch opportunities every 24 hours - 23 minutes.

Fast transfer does not allow for 24hr scrub turnaround, the next opportunity is too soon and a day will have to be skipped.

The amount of Dragon propellant does not change this.

Offline Basto

  • Full Member
  • *
  • Posts: 121
  • Salt Lake City, UT
  • Liked: 111
  • Likes Given: 137
Re: SpaceX Dragon 2 Updates and Discussion - Thread 2
« Reply #437 on: 07/18/2017 05:51 PM »

random internet speculators out there say 400-450 m/s. that seems like a lot.

superdracos can apply all of that in < 10 seconds. not that they would want to, but there will be more than enough capability to apply the delta-v quickly.


Neither are going to make rendezvous quicker.

If the Dragon is not launched at the proper time, it will take many more days for it to catch up with the ISS. 

2 day rendezvous provides for launch opportunities every 24 hours - 23 minutes.

Fast transfer does not allow for 24hr scrub turnaround, the next opportunity is too soon and a day will have to be skipped.

The amount of Dragon propellant does not change this.

I believe the disconnect here is people are misunderstanding what a "rapid" ISS rendezvous actually entails. It does not mean that the vehicle is actually traveling toward the ISS at a higher velocity. It just means you launch when the launch site is in the same plane AND ISS is at a specific angular distance to the launch site. Which means fewer launch windows.

I am pretty sure we do not want objects approaching the ISS for rendezvous with a velocity differential of 400+ M/S.

Online LouScheffer

  • Full Member
  • ****
  • Posts: 1555
  • Liked: 1734
  • Likes Given: 197
Re: SpaceX Dragon 2 Updates and Discussion - Thread 2
« Reply #438 on: 07/18/2017 05:51 PM »

random internet speculators out there say 400-450 m/s. that seems like a lot.

superdracos can apply all of that in < 10 seconds. not that they would want to, but there will be more than enough capability to apply the delta-v quickly.


Neither are going to make rendezvous quicker.

If the Dragon is not launched at the proper time, it will take many more days for it to catch up with the ISS. 

2 day rendezvous provides for launch opportunities every 24 hours - 23 minutes.

Fast transfer does not allow for 24hr scrub turnaround, the next opportunity is too soon and a day will have to be skipped.

The amount of Dragon propellant does not change this.
This is true with the current method of fast rendezvous, where you adjust the phase of ISS so it's in the right place when you launch in-plane.

But a different approach is certainly possible.  You launch when the ISS *phase* is right, then you do a plane correction to get into the ISS plane.   This is the approach used on Gemini 11, which achieved a 1.5 hour rendezvous.  Compared to the existing approach, this needs additional delta-V, to be provided by some combination of excess booster performance and payload maneuvering.  With this approach you get two opportunities each day.

Falcon 9 easily has enough raw performance to do this, if run expendable.  But if the booster does RTLS, then the margin is less and the booster may not be able to do all of the plane change needed.  In this case the amount of Dragon propellant may determine if this approach is possible.

This seems pretty unlikely, though. It's a  very different procedure, SpaceX does not currently offer  yaw steering, two day rendezvous for cargo seems fine, phasing for crewed missions only is not too much of  burden, and so on.


Offline starsilk

  • Full Member
  • ****
  • Posts: 622
  • Denver
  • Liked: 212
  • Likes Given: 40
Re: SpaceX Dragon 2 Updates and Discussion - Thread 2
« Reply #439 on: 07/18/2017 06:02 PM »

random internet speculators out there say 400-450 m/s. that seems like a lot.

superdracos can apply all of that in < 10 seconds. not that they would want to, but there will be more than enough capability to apply the delta-v quickly.


Neither are going to make rendezvous quicker.

If the Dragon is not launched at the proper time, it will take many more days for it to catch up with the ISS. 

2 day rendezvous provides for launch opportunities every 24 hours - 23 minutes.

Fast transfer does not allow for 24hr scrub turnaround, the next opportunity is too soon and a day will have to be skipped.

The amount of Dragon propellant does not change this.
This is true with the current method of fast rendezvous, where you adjust the phase of ISS so it's in the right place when you launch in-plane.

But a different approach is certainly possible.  You launch when the ISS *phase* is right, then you do a plane correction to get into the ISS plane.   This is the approach used on Gemini 11, which achieved a 1.5 hour rendezvous.  Compared to the existing approach, this needs additional delta-V, to be provided by some combination of excess booster performance and payload maneuvering.  With this approach you get two opportunities each day.

Falcon 9 easily has enough raw performance to do this, if run expendable.  But if the booster does RTLS, then the margin is less and the booster may not be able to do all of the plane change needed.  In this case the amount of Dragon propellant may determine if this approach is possible.

This seems pretty unlikely, though. It's a  very different procedure, SpaceX does not currently offer  yaw steering, two day rendezvous for cargo seems fine, phasing for crewed missions only is not too much of  burden, and so on.

seems like a useful technology to (re) develop.

Tags: