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#1360
by
scr00chy
on 17 Mar, 2019 13:27
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You're right, my number seems too low, but from the document it sounds like they're talking about Dragon 2 in general, not about its state during reentry, but who knows.
The propellant mass of 2600 kg you mentioned seems to fit better considering that Cargo Dragon uses about 1000 kg of propellant during regular operations (launches with
1290 kg and lands with "up to 20 percent of the maximum propellant load" as per the FAA doc) and that should be similar on Crew Dragon. And if an abort uses 1500 kg as per IFA document, 2600 kg of propellant total at liftoff sounds about right.
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#1361
by
groknull
on 17 Mar, 2019 16:28
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So what're these three pins on the nosecone? They look to have been exposed during reentry and not protected by some detachable cover. Maybe some interface for the CAA (they're right over the hatch)?
EDIT: Actually, reviewing orbital photos I noticed the recess is uncovered but there don't appear to be pins? So some kind of data or commanding interface for recovery ops?
Speculation:
The recess might be the atmospheric nosecone vent. The pins may be part of a plug inserted post-splashdown to prevent additional moist sea-air from circulating under the nosecone.
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#1362
by
punder
on 17 Mar, 2019 17:19
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That little hole sure caused a lot of turbulence during reentry!
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#1363
by
aviators99
on 17 Mar, 2019 17:44
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Is there a thread for the in-flight abort mission?
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#1364
by
AC in NC
on 17 Mar, 2019 17:55
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#1365
by
strawwalker
on 17 Mar, 2019 19:00
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[...] from the document it sounds like they're talking about Dragon 2 in general, not about its state during reentry, but who knows.
It is certainly possible to be overconfident in conclusions drawn from those documents, and I speak with no authority. I just mean it as a suggestion for the discrepancy between the two documents which were published around the same time, late in Crew Dragon's development, and 350 kg is a reasonable amount of propellant to consume in a mission that aborts after reaching orbit. Your reading is reasonable also.
Most of this Dragon size/mass discussion probably belongs in the Crew Dragon discussion thread rather than here, but it may be possible to explain those prop numbers other ways depending on what assumptions you make about the propellant plumbing arrangements.
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#1366
by
Vettedrmr
on 18 Mar, 2019 10:22
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Just a guess, but the pitching motion could be the rotation necessary to maintain orientation with the ISS as it rotates around the earth (it *does* keep the same relative position to the earth's surface, right?).
Have a good one,
Mike
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#1367
by
Herb Schaltegger
on 18 Mar, 2019 12:22
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Just a guess, but the pitching motion could be the rotation necessary to maintain orientation with the ISS as it rotates around the earth (it *does* keep the same relative position to the earth's surface, right?).
Have a good one,
Mike
Good guess.
Yes, ISS typically maintains LVLH (local vertical/local horizontal) orientation relative to the earth’s surface, rotating very slowly with a period of 23 hours and 56 minutes (or whatever the more precise number is). So from the Station’s perspective, the Dragon will appear to pitch up over time and periodically have to reorientate to keep its nose pointed at the docking adapter.
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#1368
by
The Roadie
on 18 Mar, 2019 12:57
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Just a guess, but the pitching motion could be the rotation necessary to maintain orientation with the ISS as it rotates around the earth (it *does* keep the same relative position to the earth's surface, right?).
Have a good one,
Mike
Good guess.
Yes, ISS typically maintains LVLH (local vertical/local horizontal) orientation relative to the earth’s surface, rotating very slowly with a period of 23 hours and 56 minutes (or whatever the more precise number is). So from the Station’s perspective, the Dragon will appear to pitch up over time and periodically have to reorientate to keep its nose pointed at the docking adapter.
Shouldn't the period equal an orbit, not a day?
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#1369
by
Herb Schaltegger
on 18 Mar, 2019 13:07
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Just a guess, but the pitching motion could be the rotation necessary to maintain orientation with the ISS as it rotates around the earth (it *does* keep the same relative position to the earth's surface, right?).
Have a good one,
Mike
Good guess.
Yes, ISS typically maintains LVLH (local vertical/local horizontal) orientation relative to the earth’s surface, rotating very slowly with a period of 23 hours and 56 minutes (or whatever the more precise number is). So from the Station’s perspective, the Dragon will appear to pitch up over time and periodically have to reorientate to keep its nose pointed at the docking adapter.
Shouldn't the period equal an orbit, not a day?
Yeah, correct. Needed more coffee before posting.
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#1370
by
ThePonjaX
on 19 Mar, 2019 01:37
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After saw the video from Nasa, poste in the update thread:
https://forum.nasaspaceflight.com/index.php?topic=47095.msg1924246#msg1924246I know is imposible but I'd like to know what Mr. Bridenstine could do if he has the absolute power.
Yes, yes, he can't because the Senate, the jobs in Alabama etc. etc. but I'd like to hear what he could do: Just cut the SLS? Funding the Starship? Design the missions to make use of available comercial rockets?
The kind of conversation which you've with a very close friend at home with a glass of wine.
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#1371
by
octavo
on 19 Mar, 2019 04:01
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Just a guess, but the pitching motion could be the rotation necessary to maintain orientation with the ISS as it rotates around the earth (it *does* keep the same relative position to the earth's surface, right?).
Have a good one,
Mike
Good guess.
Yes, ISS typically maintains LVLH (local vertical/local horizontal) orientation relative to the earth’s surface, rotating very slowly with a period of 23 hours and 56 minutes (or whatever the more precise number is). So from the Station’s perspective, the Dragon will appear to pitch up over time and periodically have to reorientate to keep its nose pointed at the docking adapter.
Doesn't ISS go into free floating mode when there is a visiting vehicle? So even movements by the crew inside could cause small changes in attitude of the ISS?
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#1372
by
CorvusCorax
on 19 Mar, 2019 06:51
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Just a guess, but the pitching motion could be the rotation necessary to maintain orientation with the ISS as it rotates around the earth (it *does* keep the same relative position to the earth's surface, right?).
Have a good one,
Mike
Good guess.
Yes, ISS typically maintains LVLH (local vertical/local horizontal) orientation relative to the earth’s surface, rotating very slowly with a period of 23 hours and 56 minutes (or whatever the more precise number is). So from the Station’s perspective, the Dragon will appear to pitch up over time and periodically have to reorientate to keep its nose pointed at the docking adapter.
Doesn't ISS go into free floating mode when there is a visiting vehicle? So even movements by the crew inside could cause small changes in attitude of the ISS?
In theory, yes. However the crew is very light compared to the total mass of the station (~420000kg ), and the impulses they impart on the structure while moving inside mostly cancel each other out over time, so they can't accumulate.
The station as a whole has a rotational momentum, so even in free drift it will keep rotating at that rate.
What might have a visible effect is the actuation of large, heavy, mobile substructures, especially those on the outside and far from the center of mass:
-Robotic arms
-Rotating solar panels and radiators ( although they were locked fixes for docking )
-Fluids circulating in the station, such as coolant. ( although steady state constant flow should cancel out )
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#1373
by
Shanuson
on 19 Mar, 2019 07:12
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Just a guess, but the pitching motion could be the rotation necessary to maintain orientation with the ISS as it rotates around the earth (it *does* keep the same relative position to the earth's surface, right?).
Have a good one,
Mike
Good guess.
Yes, ISS typically maintains LVLH (local vertical/local horizontal) orientation relative to the earth’s surface, rotating very slowly with a period of 23 hours and 56 minutes (or whatever the more precise number is). So from the Station’s perspective, the Dragon will appear to pitch up over time and periodically have to reorientate to keep its nose pointed at the docking adapter.
Doesn't ISS go into free floating mode when there is a visiting vehicle? So even movements by the crew inside could cause small changes in attitude of the ISS?
To my knowledge ISS was
not in free float when dragon docked (they highlighted that on the webcast IIRC).
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#1374
by
Alexphysics
on 19 Mar, 2019 07:55
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Just a guess, but the pitching motion could be the rotation necessary to maintain orientation with the ISS as it rotates around the earth (it *does* keep the same relative position to the earth's surface, right?).
Have a good one,
Mike
Good guess.
Yes, ISS typically maintains LVLH (local vertical/local horizontal) orientation relative to the earth’s surface, rotating very slowly with a period of 23 hours and 56 minutes (or whatever the more precise number is). So from the Station’s perspective, the Dragon will appear to pitch up over time and periodically have to reorientate to keep its nose pointed at the docking adapter.
Doesn't ISS go into free floating mode when there is a visiting vehicle? So even movements by the crew inside could cause small changes in attitude of the ISS?
Not for Dragon, the ISS attitude control was on active mode. For Soyuz it is deactivated
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#1375
by
Tommyboy
on 19 Mar, 2019 19:42
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Just a guess, but the pitching motion could be the rotation necessary to maintain orientation with the ISS as it rotates around the earth (it *does* keep the same relative position to the earth's surface, right?).
Have a good one,
Mike
Good guess.
Yes, ISS typically maintains LVLH (local vertical/local horizontal) orientation relative to the earth’s surface, rotating very slowly with a period of 23 hours and 56 minutes (or whatever the more precise number is). So from the Station’s perspective, the Dragon will appear to pitch up over time and periodically have to reorientate to keep its nose pointed at the docking adapter.
Doesn't ISS go into free floating mode when there is a visiting vehicle? So even movements by the crew inside could cause small changes in attitude of the ISS?
Not for Dragon, the ISS attitude control was on active mode. For Soyuz it is deactivated
Why this difference? Because the Dragon was unmanned, and will the ISS attitude control be deactivated during manned Dragon approaches? Or is the Dragon better in dealing with a moving target than Soyuz?
To be sure: This is not a "Russia sux, SpaceX rocks" comment, I'm genuinely curious.
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#1376
by
Alexphysics
on 19 Mar, 2019 19:50
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Just a guess, but the pitching motion could be the rotation necessary to maintain orientation with the ISS as it rotates around the earth (it *does* keep the same relative position to the earth's surface, right?).
Have a good one,
Mike
Good guess.
Yes, ISS typically maintains LVLH (local vertical/local horizontal) orientation relative to the earth’s surface, rotating very slowly with a period of 23 hours and 56 minutes (or whatever the more precise number is). So from the Station’s perspective, the Dragon will appear to pitch up over time and periodically have to reorientate to keep its nose pointed at the docking adapter.
Doesn't ISS go into free floating mode when there is a visiting vehicle? So even movements by the crew inside could cause small changes in attitude of the ISS?
Not for Dragon, the ISS attitude control was on active mode. For Soyuz it is deactivated
Why this difference? Because the Dragon was unmanned, and will the ISS attitude control be deactivated during manned Dragon approaches? Or is the Dragon better in dealing with a moving target than Soyuz?
To be sure: This is not a "Russia sux, SpaceX rocks" comment, I'm genuinely curious.
I don't know exactly the reason but it is not precisely due to it not having crew onboard, for Progress missions it happens the same as Soyuz and those don't carry crew.
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#1377
by
jarmumd
on 19 Mar, 2019 19:53
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Not for Dragon, the ISS attitude control was on active mode. For Soyuz it is deactivated
Why this difference? Because the Dragon was unmanned, and will the ISS attitude control be deactivated during manned Dragon approaches? Or is the Dragon better in dealing with a moving target than Soyuz?
To be sure: This is not a "Russia sux, SpaceX rocks" comment, I'm genuinely curious.
I don't know the technical reason why Soyuz doesn't. ISS would rather stay in control (the longer it is in drift, the more prop must be used to get back to the desired orientation). AFAIK this isn't a requirement. Concern is alignment of docking hooks and umbilical connections if station begins a large control thrust during docking.
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#1378
by
eeergo
on 19 Mar, 2019 23:24
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It might have to do with the stronger force the probe-cone SSVP-G4000 docking mechanism in the Soyuz/Progress requires a certain impact velocity and misalignments are corrected by sliding the probe on the cone surface (which will induce rotational moments).
By contrast, the newly-designed mechanism used in the IDA, International Docking System Standard (IDSS) uses the NASA version of this standard (NDS), which is an upgrade of the long-developed LIDS (NDS=iLIDS), a low-impact version of the Soviet-conceived APAS-95 - which already required lower contact velocities to engage than the SSVP. Still, Shuttle needed ISS to go on free drift, but of course it had a much more spread mass distribution and consequently torques, and APAS needed a considerable force to engage anyway.
Point is, Crew Dragon's docking mechanism requires much less moment transfer to ISS than Soyuz/Progress'.
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#1379
by
CorvusCorax
on 20 Mar, 2019 10:33
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Not for Dragon, the ISS attitude control was on active mode. For Soyuz it is deactivated
Why this difference? Because the Dragon was unmanned, and will the ISS attitude control be deactivated during manned Dragon approaches? Or is the Dragon better in dealing with a moving target than Soyuz?
To be sure: This is not a "Russia sux, SpaceX rocks" comment, I'm genuinely curious.
I don't know the technical reason why Soyuz doesn't. ISS would rather stay in control (the longer it is in drift, the more prop must be used to get back to the desired orientation). AFAIK this isn't a requirement. Concern is alignment of docking hooks and umbilical connections if station begins a large control thrust during docking.
https://www.forbes.com/sites/quora/2017/04/26/how-does-the-international-space-station-keep-its-orientation/Very relevant article for that.
