Commercial Cargo Delta V Question for ISS

[yg1968]

From Chris' article:
http://www.nasaspaceflight.com/2011/03/sts-135-preparing-srb-stacking-mission-tweaking/

“Station is worried about some of the commercial flights not getting there as soon as they thought they would, and not getting delta V. They want to go up to 215 nm, currently at 205 nm.

Commercial cargo flights do not have enough delta V? How much of a problem is that?

[Lee Jay]

From Chris' article:

“Station is worried about some of the commercial flights not getting there as soon as they thought they would, and not getting delta V. They want to go up to 215 nm, currently at 205 nm.

Commercial cargo flights do not have enough delta V? How much of a problem is that?

I think that means not getting enough delta V transferred to station.  They want to increase the altitude of the station and that requires quite a lot of propellant, since it's so big now.

[robertross]

From Chris' article:

“Station is worried about some of the commercial flights not getting there as soon as they thought they would, and not getting delta V. They want to go up to 215 nm, currently at 205 nm.

Commercial cargo flights do not have enough delta V? How much of a problem is that?

I think that means not getting enough delta V transferred to station.  They want to increase the altitude of the station and that requires quite a lot of propellant, since it's so big now.

I thought it to mean that since they are planning on re-boosting the ISS's orbit higher now, that the vehicles may not be able to get there (and likely not have sufficient margin).

[Lee Jay]

From Chris' article:

“Station is worried about some of the commercial flights not getting there as soon as they thought they would, and not getting delta V. They want to go up to 215 nm, currently at 205 nm.

Commercial cargo flights do not have enough delta V? How much of a problem is that?

I think that means not getting enough delta V transferred to station.  They want to increase the altitude of the station and that requires quite a lot of propellant, since it's so big now.

I thought it to mean that since they are planning on re-boosting the ISS's orbit higher now, that the vehicles may not be able to get there (and likely not have sufficient margin).

I guess it's not completely clear, but I read it as "Station is worried about...not getting delta V (from the commercial flights).  They want to go up to 215 nm, currently at 205 nm.

[robertross]

From Chris' article:

“Station is worried about some of the commercial flights not getting there as soon as they thought they would, and not getting delta V. They want to go up to 215 nm, currently at 205 nm.

Commercial cargo flights do not have enough delta V? How much of a problem is that?

I think that means not getting enough delta V transferred to station.  They want to increase the altitude of the station and that requires quite a lot of propellant, since it's so big now.

I thought it to mean that since they are planning on re-boosting the ISS's orbit higher now, that the vehicles may not be able to get there (and likely not have sufficient margin).

I guess it's not completely clear, but I read it as "Station is worried about...not getting delta V (from the commercial flights).  They want to go up to 215 nm, currently at 205 nm.

In 'ONE' of these threads on the site, there was a recent discussion on the original planned orbit for the ISS, and how it was going to be re-boosted (IIRC: this year) to that higher orbit. There was mention of the extra propellant to get there. I think it also discussed Progress. This might be what is now being discussed. I'm trying to find it.

Oh, and (oops) this is obviously the wrong thread for this discussion 

second edit: here's Pete's notes on what I was thinking about. Directly STS-135 related, but only his thoughts on the situation. Have to dig deeper to find the original source, and a proper thread to place it in (obviously VERY important discussion):
http://forum.nasaspaceflight.com/index.php?topic=24088.msg701583#msg701583

[mmeijeri]

I thought it to mean that since they are planning on re-boosting the ISS's orbit higher now, that the vehicles may not be able to get there (and likely not have sufficient margin).

The lower orbit is because the Shuttle would have trouble with higher orbits (because the orbiter is so heavy), not commercial launchers. There had been talk of later versions of ATV requiring less reboost / propellant transfer capability, but if they're worried about reboost the capability is still available.

[psloss]

400 km is approximately 215 n.mi.  ATV-2 was provisioned to raise the Station orbit to 400 km in a series of burns:
http://www.nasa.gov/mission_pages/station/expeditions/expedition26/iss_altitude.html

(anik has some/all of the burns on the calendar.)

Station is currently at ~ 350 km / 190 n.mi.  The higher altitude will make orbit maintenance more fuel efficient (esp. where "we" are in the Solar Cycle), but 400 km is going to impact performance for all the visiting vehicles.  The visiting vehicles that carry fuel to ISS (Progress and ATV) could still come out "ahead," since they could reduce fuel load to offset the performance hit.

[yg1968]

Thanks Philipp. That clarifies things.

[Space Pete]

Once ISS is reboosted up to 400km, it will only require 8,000 pounds of propellant a year for reboosts. At the moment, it requires 19,000 pounds of propellant. So I don't think the problem is with ISS Delta V.

I read it as the commercial vehicles may not have enough Delta V to deliver their maximum capacity payload to ISS in its higher orbit. Although ISS will require less propellant per year for reboosts, the Visiting Vehicles (VVs) will need to carry more propellant due to the higher rendezvous altitude. That means less dry cargo.

[Jim]

What is this vehicle called "Delta V" and what does it have to do with the ISS? 

[Robotbeat]

Once ISS is reboosted up to 400km, it will only require 8,000 pounds of propellant a year for reboosts. At the moment, it requires 19,000 pounds of propellant. So I don't think the problem is with ISS Delta V.

I read it as the commercial vehicles may not have enough Delta V to deliver their maximum capacity payload to ISS in its higher orbit. Although ISS will require less propellant per year for reboosts, the Visiting Vehicles (VVs) will need to carry more propellant due to the higher rendezvous altitude. That means less dry cargo.

True, but because they are not launched on pseudo-SSTO launch vehicles, the performance hit is a lot lower than for Shuttle. I think most of the vehicles will have very little problem.

8000lbs versus 19000lbs is a LOT of less logistics, too!

[Lee Jay]

What is this vehicle called "Delta V" and what does it have to do with the ISS? 

I think it's Delta IV + I, and I don't know.

[docmordrid]

What is this vehicle called "Delta V" and what does it have to do with the ISS? 

Quick!! Someone call the NY Times!!!

- Jim made a funny

[savuporo]

8000lbs versus 19000lbs is a LOT of less logistics, too!

Half of the market for commercial resupply, evaporated ..

[arkaska]

Remember that this is not something new. It has been the plan for a long time to raise the ISS orbit once shuttle retires so this reduced need for propellant has been the plan for a while.

[SpacexULA]

8000lbs versus 19000lbs is a LOT of less logistics, too!

Half of the market for commercial resupply, evaporated ..

Don't think either of the CRS teams where providing fuel on orbit, so doesn't really effect them.

[yg1968]

Once ISS is reboosted up to 400km, it will only require 8,000 pounds of propellant a year for reboosts. At the moment, it requires 19,000 pounds of propellant. So I don't think the problem is with ISS Delta V.

I read it as the commercial vehicles may not have enough Delta V to deliver their maximum capacity payload to ISS in its higher orbit. Although ISS will require less propellant per year for reboosts, the Visiting Vehicles (VVs) will need to carry more propellant due to the higher rendezvous altitude. That means less dry cargo.

That makes sense.

[robertross]

Something that maybe one of our SpaceX 'extremists'    can answer (since I'm useless at these things):

From the Falcon 9 user's guide, it can put 9358 kg in a 400km x 51.6 deg inclination circular LEO from Cape Canaveral.

Dragon masses 4200kg (dry) and can support 6000kg of up-mass to LEO with 1290 kg of flight propellant. That sounds like 11,490kg total (max), but that means it won't make it to a 400km height for ISS, which means removing upmass. Maximum upmass would then be (9358-4200-1290)=3868kg upmass capable only.

Hmmm. Sound correct?
 

[docmordrid]

IIRC ISS apogee is 355km, not 400km.  Someone chk my memory if that's wrong? 

[hop]

IIRC ISS apogee is 355km, not 400km.  Someone chk my memory if that's wrong? 

As discussed above, the plan is to boost ISS to ~400km once the shuttle missions are over. We are also (finally) entering the more active part of the solar cycle, so the cost of staying low will be higher for the next several years.

[pathfinder_01]

Dragon masses 4200kg (dry) and can support 6000kg of up-mass to LEO with 1290 kg of flight propellant. That sounds like 11,490kg total (max), but that means it won't make it to a 400km height for ISS, which means removing upmass. Maximum upmass would then be (9358-4200-1290)=3868kg upmass capable only.

Hmmm. Sound correct?
 

Might not be carring 1290kg of propellant. Dragon only needs enough propellant to rendevous with the ISS. Dragon is built to stay 2 years in space without the ISS so I would expect that it would need extra propellant for station keeping.

[Danderman]

Something that maybe one of our SpaceX 'extremists'    can answer (since I'm useless at these things):

From the Falcon 9 user's guide, it can put 9358 kg in a 400km x 51.6 deg inclination circular LEO from Cape Canaveral.

Hmmm. Sound correct?

The COTS Dragon missions don't require a payload fairing or LAS, so maybe the F9 user guide number is not valid for those missions, which might give the 10K kg payload mass for COTS missions that has been bandied about.

I was thinking that 1290 kg prop is excessive for ISS missions, but its virtually exactly the same prop load as Soyuz, adjusted for the greater Dragon mass. Soyuz has margin to achieve the 425 km altitude required for the ISS orbit, so Dragon should be OK.

[robertross]

Dragon masses 4200kg (dry) and can support 6000kg of up-mass to LEO with 1290 kg of flight propellant. That sounds like 11,490kg total (max), but that means it won't make it to a 400km height for ISS, which means removing upmass. Maximum upmass would then be (9358-4200-1290)=3868kg upmass capable only.

Hmmm. Sound correct?
 

Might not be carring 1290kg of propellant. Dragon only needs enough propellant to rendevous with the ISS. Dragon is built to stay 2 years in space without the ISS so I would expect that it would need extra propellant for station keeping.

Well that's partially correct, but you also need propellant to depart the ISS, not just rendezvous. They may offload some propellant on later missions, once all the systems are refined. They may also do some changes to increase upmass like they did with ATV-II vs. ATV-I.

[QuantumG]

There's no numbers for Dragon.. dry mass or otherwise.  The 4200kg thing is from some ancient literature before there was even one built.  Maybe after the next COTS demo they'll actually publish some real numbers.

[Lurker Steve]

8000lbs versus 19000lbs is a LOT of less logistics, too!

Half of the market for commercial resupply, evaporated ..

That means fewer Progress vehicles are needed to refuel the thrusters on the Russian side of the station.

It doesn't mean that the station will require less food, water, clean clothes, spare parts, etc that get transported up in the pressurized modules.

[Robotbeat]

8000lbs versus 19000lbs is a LOT of less logistics, too!

Half of the market for commercial resupply, evaporated ..

That means fewer Progress vehicles are needed to refuel the thrusters on the Russian side of the station.

It doesn't mean that the station will require less food, water, clean clothes, spare parts, etc that get transported up in the pressurized modules.

Quite right. Commercial resupply doesn't (or, rather, isn't supposed to) supply reboost propellant, that's only Shuttle (reboost), ATV, and Progress. This means less need for Shuttle reboost (and improved microgravity).

[arkaska]

I think he meant that the vehicles currently carrying propellant can carry other stuff instead freeing up the need for as much commercial cargo. But as I sad before, this has been the plan for a long time so if they don't raise the orbit they will need MORE vehicles going up to ISS.

[simonbp]

What is this vehicle called "Delta V" and what does it have to do with the ISS? 

I think it's Delta IV + I, and I don't know.

Yeah, a Delta IV CBC with two Extended-tank Thors slaped on either side. Now that's a rocket...

[Space Pete]

I think he meant that the vehicles currently carrying propellant can carry other stuff instead freeing up the need for as much commercial cargo. But as I sad before, this has been the plan for a long time so if they don't raise the orbit they will need MORE vehicles going up to ISS.

The commercial vehicles will need to carry MORE propellant in order to rendezvous with the ISS in its higher orbit. That means they will be able to carry LESS dry cargo than they would if ISS was in a lower orbit. If they were to carry the same amount of dry cargo, then they would need even MORE propellant.

[Robotbeat]

I think he meant that the vehicles currently carrying propellant can carry other stuff instead freeing up the need for as much commercial cargo. But as I sad before, this has been the plan for a long time so if they don't raise the orbit they will need MORE vehicles going up to ISS.

The commercial vehicles will need to carry MORE propellant in order to rendezvous with the ISS in its higher orbit. That means that they will have to carry LESS dry cargo than they would if ISS was in a lower orbit. If they were to carry the same amount of dry cargo, then they would need even MORE propellant.

What difference in payload? 1-5%? Dragon should have no problem, since Dragon only has to do about 1667kg per flight, while it has a capacity far more than double that (if you include both pressurized and unpressurized). If cargo is volume-limited, then this should make no difference.

[arkaska]

The commercial vehicles will need to carry MORE propellant in order to rendezvous with the ISS in its higher orbit. That means they will be able to carry LESS dry cargo than they would if ISS was in a lower orbit. If they were to carry the same amount of dry cargo, then they would need even MORE propellant.

My point was that this reduced need of propellant will not mean they have a have more up-mass then needed since this have been the plan for a long time.