1970 SSTO Concept – NASA Ames "MAD-OART"

[HMXHMX]

For historical interest (and in connection with a discussion on the SpaceX "Starship" (BFS) concept in another forum topic) here's an interesting working paper written in 1970 by Ed Gomersall from the NASA Ames Mission Analysis Division ("MAD").

[tyrred]

Man, what a find...  16 annular aerospikes, wowee!  And those 7-segment 120" strap-on SRM's for the "lunar mission", wonder what cosine losses due to the attachment angles would be, or if it would have mattered much.   

[HMXHMX]

Man, what a find...  16 annular aerospikes, wowee!  And those 7-segment 120" strap-on SRM's for the "lunar mission", wonder what cosine losses due to the attachment angles would be, or if it would have mattered much.   

While the motors were attached to the sidewall at an angle, the nozzles themselves could have been canted against that angle, at least partially, mitigating the losses.  (Personally, I'm not a fan of big solids, but Ed added them to pretty much everything he worked on.  I'm sure these would have needed TVC at the nozzles, unlike for example Delta, and more like the Shuttle SRB.)

[Proponent]

And those 7-segment 120" strap-on SRM's for the "lunar mission", wonder what cosine losses due to the attachment angles would be, or if it would have mattered much.   

What would worry me about the SRM's is the risk of catastrophic failure.  Large solids of the era had about a 0.5% failure rate (see the report attached to this post).  Strapping on six for a lunar mission would raise the probability of catastrophe by about 3%.

Nitpick:  I believe the 1205's are 5-segment SRM's.

[tyrred]

And those 7-segment 120" strap-on SRM's for the "lunar mission", wonder what cosine losses due to the attachment angles would be, or if it would have mattered much.   

What would worry me about the SRM's is the risk of catastrophic failure.  Large solids of the era had about a 0.5% failure rate (see the report attached to this post).  Strapping on six for a lunar mission would raise the probability of catastrophe by about 3%.

Nitpick:  I believe the 1205's are 5-segment SRM's.

The document mentioned them as 7-segment on page 20, I believe, but yeah... solid motor catastrophes are never good, but always spectacular.

[Proponent]

The document mentioned them as 7-segment on page 20, I believe....

Page 20 mentions 7-segment SRM's in a general way:

The recent firing tests of the seven-segment 120-inch SRM involved the thrust levels required for the study vehicle,

but 5-segment motors are specified for the vehicle on page 3:

A thrust augmented mode operation is also possible with the basic shuttle core vehicle.  By utilizing an interchangeable forward skirt, thrust augmentation is possible without structural modification to the basic shuttle core vehicle.  Strap-on 5-segment 120" SRM's or other thrustors are used for thrust augmentation.

Measuring the lengths of the SRM's that appear in Figure 20, I get 89 feet, which is closer to the 85 feet that Encyclopedia Astronautica quotes for the UA-1205 than to the 125 feet that it quotes for the UA-1207.  Finally, Figure 3 refers to "1205 M SRM strap-ons" (though I can't say I know what the 'M' means).

[Nomic]

Interesting read, very much an evolution of the amllv study.