5.5 Segment Ares I

[rcaron]

I was at the Joint Propulsion Conference yesterday where there was a whole track of presentations related to Ares. I asked the Ares V presenter about the 5.5 steel (now baselined) and the composite w/ PBAN and whether either of those would be retrofitted onto Ares I as a later upgrade. My thoughts were akin to the lunar nozzles.

Both the presenter and the Ares I presenter had a very enthusiastic NO. The trouble primarily stems from how the Ares I booster already has a reentry profile ~50% 'hotter' than current shuttle (120kft shuttle apogee, 190kft ares I, Mach 4 vs Mach 6 respectively). TPS would start becoming a real concern if you increased the booster performance any further. The parachute system is also struggling to keep the velocity at impact the same as shuttle, since any higher would increase damage and impact reusability.

[kraisee]

So it looks like it will be divergent SRB's after all.   Interesting.

If they end up with steel 5.0-seg for Ares-I and composite 5.5- or 6.0-seg disposables for Ares-5/6/7 I'm thinking the board at ATK won't be very upset at all.

Ross.

[rcaron]

So it looks like it will be divergent SRB's after all.   Interesting.

And I mentioned that this architecture was sold to us not only on shuttle commonality but also between the Ares vehicles. He said that while they would technically be divergent they would share substantial commonality with respect to manufacturing and ground handling and the like. Of course, this is only true if they stick with the steel 5.5s and not the composite PBANs.

He mentioned that there is a directive from somewhere up above to keep the composite PBANs in the tradespace for the foreseeable future. According to the charts, they do offer quite a deal more lunar payload capability, on the order of 3mT over the  5.5s if i remember correctly. Wish I took more notes, but those charts were packed!

[renclod]

So it looks like it will be divergent SRB's after all.   Interesting.

If they end up with steel 5.0-seg for Ares-I and composite 5.5- or 6.0-seg disposables for Ares-5/6/7 I'm thinking the board at ATK won't be very upset at all.

Ross.

I'm thinking that, if the composite overwrapped case/HTPB booster gets selected for Ares V, the "board at ATK" has a surprise coming their way in the form of "competitive acquisition environment for booster"

As opposed to "single source".

http://www.lpi.usra.edu/pss/presentations/200806/12neal.pdf

[Herb Schaltegger]

Take a look at the makeup of the ATK Board . . .

http://www.atk.com/CorporateGovernance/corpgov_boardofdirect.asp

And then realize that most of these folks sit on more than one (many Directors sit on three or more corporate booards).

[Antares]

rcaron, who were the presenters for Ares at JPC this year?  Poor MSFC tech writers do all the work and the civil servants put their names on the papers.

[gospacex]

Nice work, thanks for posting.
I think that it actually looks better than the 5 seg. version... "better proportioned."

Well, the best shape for tanks to have highest possible mass ratio is a sphere, but it is difficult to build. Next best is a "fat" cylinder, which is much easier to build, but it has too big a cross section and creates lots of drag when flown as a rocket. So you need to stretch it, trading worsening mass fraction for improving aerodynamics.

I don't know what proportions are deemed optimal in this regard. I do know, however, that most LVs, as they evolve, chose to stretch the tanks instead of widening them, as this is somewhat easier on infrastructure. Thus most existing LV's are evolved to be "too tall and thin".

I think Atlas Phase 2 is one which is closest to optimal width/height. Look at the attached picture - it is quite stubby. Got to have good mass fractions on both stages and does not stand excessively tall on launch pad.

In this regard, Ares I looked awful from the start. Long, thin (=> bad mass fraction) 1st stage with ugly (IMHO) "hammerhead" second stage. 5 seg only made it worse.

[rcaron]

rcaron, who were the presenters for Ares at JPC this year?  Poor MSFC tech writers do all the work and the civil servants put their names on the papers.

Steve Creech did the Ares V refinements presentation (AIAA 2008-4981)
Tomas Byrd did the J-2X ( -4980)
Charles Nola did Ares I avionics ( -4898)
Teresa Vanhooser did the Ares I booster ( -4895)

unfortunately I don't recall who did the Ares I upper stage.  Sorry to hear all these people use ghost writers...

[rcaron]

whoops. just noticed i err'd wrt to the composites. they (clearly) use the new HTPB where the steels use the legacy PBAN. Hope I didn't confuse anybody!

Some other notes:
Current baseline is 51.0.48 (5.5 steel PBAN, 6 engine core)
composite variant 51.0.47 (5.0 composite HTPB, 6 engine core) to be decided upon at Constellation Lunar SRR in 2010

the presentation renclod linked above from LPI appears virtually identical to what was presentated at JPC

[kook59]

   Shuttle SRB sep occurs at 150k ft. Why not solve the 5.5 seg reentry problem by not recovering the SRBs. Somewhere I read it was questionable if it saved any money anyway. How much payload would be gained with a 5.5 seg booster and no parachutes? How would 5.5 seg affect the T.O. problem?

[Jim]

   Shuttle SRB sep occurs at 150k ft. Why not solve the 5.5 seg reentry problem by not recovering the SRBs. Somewhere I read it was questionable if it saved any money anyway. How much payload would be gained with a 5.5 seg booster and no parachutes? How would 5.5 seg affect the T.O. problem?

Because the company line that SRB's are "safer" hinges on recovery and post flight inspection.

[TrueBlueWitt]

Some interesting stuff here

from last slide..

1:37000 LOC for Ares V.. 

Considering it doesn't carry a crew.. how exactly did they calculate that?