"Tandel Missile" design with engines forward of their fuel tanks

Question

Whilst looking for something else entirely, I came across this amazing looking rocket design mentioned in passing on this nasaspaceflight.com forum page, talking about the San Diego Air and Space Museum Photo Archive:

Searching for "Tandel missile" doesn't seem to have turned up anything relevant. The forum users suggested it was a proposed Atlas missile design.

The use of forward-mounted "second stage" engines that would apparently operate whilst the first stage rockets were running too seems fairly eccentric to me, and isn't a design I've come across before. I understand this was the 50s and people were throwing all sorts of stuff at the wall to see if it would stick, but this just stands out as unusual.

Was this arrangement of rockets ever used anywhere? Were any designs using this rocket placement ever seriously considered? What intoxicants might the engineers have been using whilst coming up with this design?

Answer 1

I can't think of a production missile or launcher that used this setup, but it's not a crazy idea.

One of the major drivers for the final "stage-and-a-half" design of the Atlas, with its single stage of tankage and drop-off booster engines, was that air-starting an engine was considered risky in the mid-1950s. Convair's final Atlas design solved this by putting the booster and sustainer engines side by side, and igniting all three at once. If the three engines didn't all ignite at once, they'd be shut down before liftoff, and the rocket would (hopefully) be saved for another try (maybe more of a consideration for test flights than for production units; if an ICBM doesn't fly when it's asked to, it probably won't be useful later).

This "Tandel" missile avoids the air-start problem as well, and has the additional advantage that it does get to drop empty tankage at staging, unlike the Atlas. asdfex's analysis is correct: there's a drag penalty and the mass of the extra plumbing and heat shielding, but the elimination of dead engine weight and interstage should more than cover that. A crossfeed system that effectively fuels the second stage engines from the first stage tankage gives a further performance advantage; the first stage can be dropped earlier in the ascent.

The Sea Dragon super-heavy launcher concept had something slightly similar: small thrusters on the second stage would fire throughout the first-stage burn for attitude control, but there was also a large second-stage engine that wasn't ignited until staging. Sea Dragon was only ever built and flown in CGI, for the alternate-history TV series For All Mankind.