Constellation program

[Satanic Mechanic]

I have been wondering about the cargo vehicle.  I read that the goal is 125 metric tons into LEO and that an improved SRB will be used. I can;t find much info on the NASA site.
Here are my questions:
Will the SRB be longer with more segments?  Anyone have numbers on the new SRB?  I would like to know the numbers because I am trying to figure out how much mass could be hauled to LEO and GEO if two more SRB's were added ( four total).
Will the current transporter (crawler) be changed to accomodate the cargo vehicle?

Thanks,

SM

[Bob B.]

A 5-segment SRM is planned for the CaLV; the current Shuttle uses a 4-segment version.  The following web page has the specs for both the CaLV and CLV as released last year; however the data is already outdated:

http://www.braeunig.us/space/specs/shutderv.htm

The design changes I'm aware of include the following:

CLV (Crew Launch Vehicle)
** The 1st stage will be a 5-segment SRM instead of a 4-segment.  The 4-segment was originally proposed because it could be ready to fly sooner.  However, when the schedule for the CEV slipped, NASA decided to go with the preferred 5-segment.
** The 2nd stage will use a J-2 engine instead of a SSME.  This way the SSME does not have to be modified for air-start capability.  Furthermore, the more powerful 5-segment 1st stage allows for use of the less powerful 2nd stage engine without diminishing payload capability.

CaLV (Cargo Launch Vehicle)
** The first stage will use the RS-68 engine in lieu of the SSME, though I don't know how many RS-68s are proposed.  The RS-68 is a much less expensive engine and is easier to mass produce.  However, this engine is less efficient than the SSME with a lower specific impulse.
** Because of the lower specific impulse of the RS-68, more propellant will be carried in the 1st stage core.  Because the height of the vehicle is limited by the size of the Vehicle Assembly Building, it is not possible to stretch the core to accommodate the extra propellant.  Therefore, the core diameter has been changed from 8.4 meters to 10.0 meters.

[Satanic Mechanic]

Bob,
Thanks for the numbers and I am using your page of equations too.  I will use your numbers anyway for my curiosity even though they are not using the SSME for the CaLV.  Do you agree that the mass of the CaLV with four SRB's is 3,004,880kg and the thrust would be 70,266.5kN?

Also, what do you consider LEO with your equations?  300km?

I am trying to find out how much could be hauled up to the ISS and if a NERVA that could go to Mars could be hauled up in one shot.

Thanks,

SM

[Bob B.]

Do you agree that the mass of the CaLV with four SRB's is 3,004,880kg and the thrust would be 70,266.5kN?

I agree with the thrust but not the mass.  The total launch mass of the CaLV is given as 2,900,288 kg (including payload).  Add two more SRMs at 751,220 kg each and you have,

2,900,288 + 2 * 751,220 = 4,402,728 kg

Also, what do you consider LEO with your equations? 300km?

I generally consider the minimum orbit 185 km (100 nautical miles), which is a figure commonly seen in NASA literature.  This altitude is good for a short duration parking orbit, but I'm not sure how long a payload can loiter in that low an orbit before decaying.  A higher orbit will probably be necessary if you want to hang around for a few months.

I see the orbit given for CLV and CaLV LEO performance is 56 X 296 km.  NASA is apparently planning to use a launch profile similar to the Space Shuttle, where the engines are cut off at a relatively low altitude and the vehicle then coasts 1/2 orbit to apogee, where a circularization burn is performed.  Without the circularization burn the vehicle will dive into the atmosphere and burn up as it comes back around to perigee.  It appears to me like NASA is planning to park the cargo in a 296 km orbit, so your 300 km figure looks good.

Just for your information, the ISS orbit varies from about 350-407 km.  The orbit is pretty close to circular, but it decays over time and has to be reboosted to a higher orbit by the Space Shuttle.  (I'm not what was done about reboosting while the Shuttle was grounded.  Evancise?)  Also note that the ISS orbit has an inclination of 51.6 degrees.  The listed CaLV performance is for a 28.5 degree orbit.  Payload performance to the ISS would be somewhat less because of the higher inclination; though I don't think there are plans for reaching the ISS with the CaLV.

[Satanic Mechanic]

Thanks Bob,
I see where I went wrong with the mass, I listed the mass of the four SRB's and forgot to include the CaLV.

SM

[Bob B.]

I see where I went wrong with the mass, I listed the mass of the four SRB's and forgot to include the CaLV.

I don't think that would work very well, but it ought to move like a bat out of hell.

For your masses, I'd use the burnout mass of each stage plus the useable propellant.  I get the following:

SRMs:  751,220 * 4 = 3,004,880 kg
Stage 1:  97,640 + 1,004,892 = 1,102,532 kg
Stage 2:  22,063 + 207,695 = 229,758 kg
Fairing:  4,773 kg
TOTAL:  4,341,943 kg

Since you're going to have a bigger payload than the CaLV, you might want to increase the mass of the fairing (maybe in the same proportion as the payload increase).

Here's something else to consider:  The 2nd stage of the CaLV is made to operate like the S-IVB of the Saturn V, i.e. it provides the final impulse during launch and then re-ignites in orbit for TLI or TMI.  If your redesigned vehicle is being used solely as a heavy launcher to boost large payloads to LEO, then the 2nd stage is probably underpowered.  I recommend adding two more J-2 engines for a total of four.  This will provide twice the thrust and half the burn time, which is probably better for your application.  I'm not sure what the mass of the new J-2S+ variant is, but the original J-2 had a mass of 1,578 kg/each.

[Satanic Mechanic]

You are right about the fairing.  I looked at the diameter the payload can be and it is too small, 7.4 meters.  Some of the NERVAs vary in size from 9 meters to 12 meters in diameter.  If NASA was to launch something like that with those sizes, the payload shroud would have to be enlarged like some of the Titans 3's.

SM

[Ottawan]

Bob, do they not also use the Progress vehicle engines to boost the station when the Shuttle is not available?

[Bob B.]

Bob, do they not also use the Progress vehicle engines to boost the station when the Shuttle is not available?

Using the Progress vehicles is the only option I can see with the such long delays between Shuttle flights, though I can't say for sure they are used this way.  The Progress' propulsion is tiny compared to the Shuttle's, but every little bit helps.  Even a delta-v of just 1 m/s* is enough to raise the orbit about 1.76 km**.

* In two burns of 0.5 m/s each 1/2 orbit apart.
** Based on an initial orbit of 380 km.

[evancise]

Bob, do they not also use the Progress vehicle engines to boost the station when the Shuttle is not available?

Using the Progress vehicles is the only option I can see with the such long delays between Shuttle flights, though I can't say for sure they are used this way.  The Progress' propulsion is tiny compared to the Shuttle's, but every little bit helps.  Even a delta-v of just 1 m/s* is enough to raise the orbit about 1.76 km**.

* In two burns of 0.5 m/s each 1/2 orbit apart.
** Based on an initial orbit of 380 km.

Almost all of ISS' reboosts are done using the Progress.  Most reboosts are on the order of 1 - 5 m/s.  While it's true that without doing a reboost the ISS would enter the atmosphere, that's usually not the driver for doing a reboost.  The ISS is a pretty busy spaceport - lots of Soyuz, Progress, and (hopefully) Orbiters coming and going.  In order to setup launch windows, the ISS' orbit must be phased correctly so it will be in the right orbital location for docking.  They do this by performing phasing burns, which are small reboosts.  So they do more reboosts per year than they'd have to for altitude considerations alone.

Most reboosts use the Progress attitude control thrusters, however larger burns are done using the Progress main engines.  When there is no Progress docked to the Service Module (SM) aft, the SM's two (or just one of the two) main engines could also be used to perform a reboost.  Finally, the Orbiter does generally perform a reboost of ISS during a docked mission.  Due to the fact that a majority of the Orbiter's thrusters cannot be used when docked (due to concerns of plume impacts on ISS), they don't really get much more delta V out of the Orbiter than they do the Progress or SM.  The largest benefit is that it uses Orbiter propellants, not the limited supply that is maintained on ISS.

Ed

[Bob B.]

Thanks, Ed.  I was hoping you'd read this thread and set me straight.

I knew the Shuttle did reboosts only because I've read about it in some of the Shuttle mission descriptions.  I had no idea though that it was done so frequently or for the reason you described.

I don't know too much about the Progress ferries.  How often are they launched?  Once they arrive, about how long do they remain docked to the station?  Do they only undock when a new one is about to arrive?  What happens then; do they deorbit and reenter over the ocean?  About how much delta-v can the station get out of one of them? 

I've also seen a lot of different numbers for the altitude of the ISS.  What is its normal range of altitudes?

Thanks in advance for your time.

[evancise]

Thanks, Ed.  I was hoping you'd read this thread and set me straight.

Glad to be able to contribute!

I don't know too much about the Progress ferries.  How often are they launched?

About once every 4 to 6 months depending on the logistics supply needs of ISS vs. the assembly/turnout capability of RSC-Energia.

Once they arrive, about how long do they remain docked to the station?  Do they only undock when a new one is about to arrive?

They remain docked typically about 6 months, which is the certified on orbit lifetime for a Progress.  They may undock sooner if all the Progress supplied logistics (propellant, air, O2, water, etc.) has been used or transferred to ISS.  If there are two Progress docked to ISS, one will depart a few days prior to launch of the next one.  There must be a place for the new one to dock prior to launching the new one.

What happens then; do they deorbit and reenter over the ocean?

Yup, they deorbit and are spread in fine pieces across the depths of the Pacific.  Prior to undock they're filled with garbage and components no longer needed on ISS and items that don't need to return on the Shuttle or Soyuz.  These are then burned up on entry.

About how much delta-v can the station get out of one of them? 

Sorry to not be able to give you a specific answer, but I hear it all depends on how much propellant the Progress comes up with.  It has two prop systems - one for its own stand alone flight (prior to docking and after undocking) and a resupply system that is used while it's docked.  A tradeoff is done with respect to the resupply system in that unused prop is transferred to tanks on the ISS.  So the answer to your question varies quite a bit based on the particular timing of the Progress mission.

Something else that's kind of cool is that early this year they increased the traffic a bit by keeping 2 Progress docked to ISS instead of just one.  It's really added to the logistics and prop capabilities and flexibility of ISS. 

I've also seen a lot of different numbers for the altitude of the ISS.  What is its normal range of altitudes?

Usually, the ISS is between 190 - 210 nmi (352 - 389 km). 

Thanks in advance for your time.

Any time. 

[Bob B.]

Thanks again, Ed.  Sorry to hijack your thread, SM.

[Satanic Mechanic]

Thanks again, Ed.  Sorry to hijack your thread, SM.

That's OK, we have all pulled a "Tomcat" a few times.
Well I have two sheets of paper with equations, I came up with the liftoff velocity of my Super CaLV and I could not believe it at first but I forgot to include the payload weight.  I was going no where fast!  I am trying to find out if I can get 200 metric tonnes into LEO with this setup.

SM

[Bob B.]

I am trying to find out if I can get 200 metric tonnes into LEO with this setup.

I'll scratch out some calculations as well and then we can compare notes later after we both have an answer.