SpaceX COTS Demo 2 Updates

[Lars_J]

This is why we had 135.

The "reason" for STS-135 was to continue to supply ISS in the manner that the orbiter was designed to do while ALSO bring equipment back home. 

While true we have been carrying more and more due to the slips in the CRS schedules and to give ISS some padding for both standard supplies and actual ISS science, it did NOT relieve ISS from any additional re-supply flights.  Otherwise, there would have been zero point in launching Progress in the first place. 

Yes, and Dragon will of course not be able to cover one of Progress's critical capability - reboost. Only ATV can do that. When does the next ATV launch? Latest reports indicated it was already down in Korou.

[peter-b]

Yes, and Dragon will of course not be able to cover one of Progress's critical capability - reboost. Only ATV can do that. When does the next ATV launch? Latest reports indicated it was already down in Korou.

IIRC that's not that all that critical at the moment, as over the last few months the ISS has been raised to a significantly higher post-assembly orbit where there is reduced drag. It can no doubt wait until the next visit of ATV or Progress.

As far as I know, cargo Dragon won't be able to take part in reboost ops in the foreseeable because of the geometry of its berthing location on the station.

So no need to panic? I'm happy to be corrected on both these points. ;-)

[Namechange User]

This is why we had 135.

The "reason" for STS-135 was to continue to supply ISS in the manner that the orbiter was designed to do while ALSO bring equipment back home. 

While true we have been carrying more and more due to the slips in the CRS schedules and to give ISS some padding for both standard supplies and actual ISS science, it did NOT relieve ISS from any additional re-supply flights.  Otherwise, there would have been zero point in launching Progress in the first place. 

Yes, and Dragon will of course not be able to cover one of Progress's critical capability - reboost. Only ATV can do that. When does the next ATV launch? Latest reports indicated it was already down in Korou.

ISS has thrusters for reboost.  Typically, they just do not like using the prop because that prop is also there for attitude hold in the event the CMGs go down, etc. 

A Soyuz could also be repositioned and push the stack along if it really came to it. 

[starsilk]

This is why we had 135.

The "reason" for STS-135 was to continue to supply ISS in the manner that the orbiter was designed to do while ALSO bring equipment back home. 

While true we have been carrying more and more due to the slips in the CRS schedules and to give ISS some padding for both standard supplies and actual ISS science, it did NOT relieve ISS from any additional re-supply flights.  Otherwise, there would have been zero point in launching Progress in the first place. 

Yes, and Dragon will of course not be able to cover one of Progress's critical capability - reboost. Only ATV can do that. When does the next ATV launch? Latest reports indicated it was already down in Korou.

Progress/ATV don't actually 'do' the reboost, right? they supply fuel to the Zvezda engine.

I'm guessing it would be difficult (or impossible) to supply fuel from a Dragon (on the US segment) to Zvezda? and Dragon's draco engines are too small to do the reboost itself?

[LegendCJS]

This is why we had 135.

The "reason" for STS-135 was to continue to supply ISS in the manner that the orbiter was designed to do while ALSO bring equipment back home. 

While true we have been carrying more and more due to the slips in the CRS schedules and to give ISS some padding for both standard supplies and actual ISS science, it did NOT relieve ISS from any additional re-supply flights.  Otherwise, there would have been zero point in launching Progress in the first place. 

Yes, and Dragon will of course not be able to cover one of Progress's critical capability - reboost. Only ATV can do that. When does the next ATV launch? Latest reports indicated it was already down in Korou.

Progress/ATV don't actually 'do' the reboost, right? they supply fuel to the Zvezda engine.

I'm guessing it would be difficult (or impossible) to supply fuel from a Dragon (on the US segment) to Zvezda? and Dragon's draco engines are too small to do the reboost itself?

Progress/ATV use their engines in the re-boosts.  They try to keep the number of engine starts and burn time on the permanent station motors (Zvezda) to a minimum because those resources are finite.

[Namechange User]

I'm guessing it would be difficult (or impossible) to supply fuel from a Dragon (on the US segment) to Zvezda? and Dragon's draco engines are too small to do the reboost itself?

Impossible. 

[starsilk]

I'm guessing it would be difficult (or impossible) to supply fuel from a Dragon (on the US segment) to Zvezda? and Dragon's draco engines are too small to do the reboost itself?

Impossible. 

I assume you're talking about the fuel transfer?

what about doing the reboost itself, given extra fuel, and presumably docked to a port which allows it to thrust through the ISS center of gravity? CBM is presumably tough enough, given it was designed for attaching station components.

I realize the 'deorbit' thrusters on dragon are on the nose, so you'd end up using angled thrusters and getting cosine losses.

[Namechange User]

I'm guessing it would be difficult (or impossible) to supply fuel from a Dragon (on the US segment) to Zvezda? and Dragon's draco engines are too small to do the reboost itself?

Impossible. 

I assume you're talking about the fuel transfer?

what about doing the reboost itself, given extra fuel, and presumably docked to a port which allows it to thrust through the ISS center of gravity? CBM is presumably tough enough, given it was designed for attaching station components.

I realize the 'deorbit' thrusters on dragon are on the nose, so you'd end up using angled thrusters and getting cosine losses.

Yes, Dragon is not equiped with that capability and neither is ISS equiped with the ability to get prop from the US segment and transfer it to the Russian segment.

Reboosting with Dragon from a CBM introducing many, many questions that need to be resolved (stress on stack, maneuver to attitude and power generation/cooling concerns, etc) at rather high cost and effort when it is not required.

As I mentioned earlier, ISS reboost can be performed with the Russian segment thrusters.

[Robotbeat]

This is why we had 135.

The "reason" for STS-135 was to continue to supply ISS in the manner that the orbiter was designed to do while ALSO bring equipment back home. 

While true we have been carrying more and more due to the slips in the CRS schedules and to give ISS some padding for both standard supplies and actual ISS science, it did NOT relieve ISS from any additional re-supply flights.  Otherwise, there would have been zero point in launching Progress in the first place. 

Yes, and Dragon will of course not be able to cover one of Progress's critical capability - reboost. Only ATV can do that. When does the next ATV launch? Latest reports indicated it was already down in Korou.

Progress/ATV don't actually 'do' the reboost, right? they supply fuel to the Zvezda engine.

I'm guessing it would be difficult (or impossible) to supply fuel from a Dragon (on the US segment) to Zvezda? and Dragon's draco engines are too small to do the reboost itself?

Keep in mind that ISS was recently reboosted quite high, thus the rate of its orbital decay is much lower and it has a lot more margin... If left to decay without any more reboosts at all, it'd take about two years to get down to the same altitude it was orbiting at the end of May this year.

Fuel can only be transferred to Zvezda through Russian docking ports. Dragon has nothing even close to that capability. Dragon's thrusters are theoretically capable of it, but I highly doubt they are cleared for any such action. You'd have to be careful about plume impingement, etc (which may be a serious problem for Dragon, based on where its thrusters are).

Orbital's Cygnus might be another matter, but again, it'd have to be very carefully analyzed. Level of thrust isn't necessarily the issue (though a very long thrusting period may be required, which interrupts sensitive experiments), since the Oberth effect is basically negligible for such small delta-v.

[Namechange User]

Orbital's Cygnus might be another matter, but again, it'd have to be very carefully analyzed. Level of thrust isn't necessarily the issue (though a very long thrusting period may be required, which interrupts sensitive experiments), since the Oberth effect is basically negligible for such small delta-v.

No, as I mentioned it is a integrated vehicle certification and operations concern. 

[peter-b]

Also, as I mentioned earlier, the ISS has been boosted to its post-assembly altitude: http://forum.nasaspaceflight.com/index.php?topic=25702.msg797798#msg797798

[starsilk]

Reboosting with Dragon from a CBM introducing many, many questions that need to be resolved (stress on stack, maneuver to attitude and power generation/cooling concerns, etc) at rather high cost and effort when it is not required.

As I mentioned earlier, ISS reboost can be performed with the Russian segment thrusters.

I'm not sure I'd agree that the capability is 'not required'. there have been plans for a (US) ISS reboost module to cover the possibility of the Russian segment (or vehicles) being unable to do the job.

seems like doing the work to 'certify' one of the new commercial US vehicles to do the job would be prudent (and it may be that Cygnus is better suited to the task, due to its shape).

[starsilk]

Also, as I mentioned earlier, the ISS has been boosted to its post-assembly altitude: http://forum.nasaspaceflight.com/index.php?topic=25702.msg797798#msg797798

yeah, that's one piece of good news.

[Namechange User]

Reboosting with Dragon from a CBM introducing many, many questions that need to be resolved (stress on stack, maneuver to attitude and power generation/cooling concerns, etc) at rather high cost and effort when it is not required.

As I mentioned earlier, ISS reboost can be performed with the Russian segment thrusters.

I'm not sure I'd agree that the capability is 'not required'. there have been plans for a (US) ISS reboost module to cover the possibility of the Russian segment (or vehicles) being unable to do the job.

seems like doing the work to 'certify' one of the new commercial US vehicles to do the job would be prudent (and it may be that Cygnus is better suited to the task, due to its shape).

Yes, I'm familar with the prop module.  It was cancelled circa 2001.  The orbiter reboosted the ISS many times, and, the orbiter was ready to be modified with lines and QDs to re-supply the US prop module if that would have continued. 

I didn't say ISS reboost was not required, meaning ever.  I said it is not required for the Dragon or any other vehicle to do it *right now*.  ISS has thrusters for this purpose and can be used IF necessary. 

[Jim]

1.  I'm not sure I'd agree that the capability is 'not required'. there have been plans for a (US) ISS reboost module to cover the possibility of the Russian segment (or vehicles) being unable to do the job.

2.  seems like doing the work to 'certify' one of the new commercial US vehicles to do the job would be prudent (and it may be that Cygnus is better suited to the task, due to its shape).

1.  That was eons ago and not applicable to today.

2.  No, not if it is not viable.

a.   shape has nothing to do with one or the other
b.  They don't carry propellant for reboost, only enough to do their mission.

[peter-b]

b.  They don't carry propellant for reboost, only enough to do their mission.

Of course, in the period between Dragon escape capability being introduced and Dragon propulsive landing being introduced, Dragon will carry excess propellant to the ISS that could be used for reboost.

[Comga]

However, I wouldn't be surprised if the November Dragon actually carries low-value bulk supplies for the ISS, on the basis that if it berths successfully it'll ease the situation, and if it fails then it won't make matters worse.

The Progress manifest included a lot of the "three T's". 367 kg "Equipment to the US segment including food, hygiene," etc,  66 kg of "Medical equipment, clothes, personal hygiene", etc. More additional food (257 kg) than fuel (250 kg).  Even more water (420 kg + 44 kg).

Cargo list.

[Comga]

Hardware, lots and lots of hardware:

http://www.nasa.gov/pdf/580727main_4%20-%20Lindenmoyer%20COTS%20Status_508.pdf

Lovely pictures.

I do see that there is at least the "starboard" window, here to the right of the hatch.  Perhaps the other window is there too, now uncovered by what may have been something temporary.  The suface looks different than in the pervious photos.

And look at that unpresurized volume.  How they plan to fit the LAS Super Dracos in there is beyond me.

[Comga]

Hardware, lots and lots of hardware:

http://www.nasa.gov/pdf/580727main_4%20-%20Lindenmoyer%20COTS%20Status_508.pdf

Also, the schedule on slide 7 gives us more data points for the "SpaceX Time Dialation Factor".  2.3X and 2.0X for the accomplished milestones. 2.2X and 1.9X if they get the FRR and COTS-2 done to the current schedule.  In other words, keeping the current launch date for COTS-2/3 requires a reduction in the delays when compared to historic data.

[Jason1701]

Suffredini said that Dragon may carry 800 lbs of cargo on COTS 2. Why not carry a more CRS-sized load?