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Battle for the space shuttle (2)
shape of things to come

"...the shape of the individual shuttle stages fell in to two generic categories - lifting bodies and ballistic bodies.
The main differences between these categories were in their aerodynamic characteristics and landing modes.

For screening purposes it was assumed that lifting bodies were good flying machines capable of delivering large amounts of crossrange or fly-back range either through hypersonic glide or subsonic powered cruise. Their complex shapes and lifting surfaces also make them inefficient propulsive machines.

Ballistic vehicles were assumed to be just the opposite: efficient propulsive vehicles but poor flying machines. As a consequence ballistic vehicles must use propulsion to achieve crossrange where it is required - notably for the Air Force mission.

The current shuttle concept - configuration 4 - is a two stage lifting body launch vehicle with integrated crew and cargo systems.

If the lifting body first stage is replaced by a ballistic booster, configuration 2 results.
If the lifting body orbiter is replaced by a ballistic orbiter, the result is configuration 7.

Concept 3 is the case where both stages are ballistic.

 Recoverable ballistic systems have been studied to a fair degree in the past, but were usually limited to large payload, single-stage-to-orbit systems.
We found very little, if none, past proposals for two stage, ballistic vehicles. (hello, SpaceX and Kistler – F9R and K-1)

The blunt shape of the ballistic vehicles enables relatively high mass fractions to be attained.
The geometry presents a good configuration for propellant packaging, and there are no heavy winged surfaces

 When analyzing two stage vehicles in which the first stage is ballistic, a unique problem exists in the recovery of that stage. A possibility is to execute an impulsive maneuver immediately after staging that would put the booster on a high lofted trajectory ending back at the launch site. This is called impulsive return to the launch site, or more commonly, lob-retro.

 Vertical landing is accomplished similar to the Lunar Module or Surveyor by firing the main engines to remove the terminal velocity and to allow some hover and translation time.

Ballistic vehicles require hover time for vertical landing. About 20 seconds was considered sufficient.

This assumption is contingent on the use of a ground beacon at the landing site which provides a cooperative navigation and guidance system. Without such a beacon landing errors would probably be on the order of two nautical miles or less as experienced in Apollo landings (...)

Four of the concepts studied warrant further investigation.
They consist of
the two stage lifting concept - currently the favoured approach for the shuttle
- a single-stage-to-orbit booster with a separate lifting body orbiter and two stage ballistic vehicles with both separate and integrated crew and cargo systems.

In general, it can be said that the two stage ballistic vehicles are quite light and have low sensitivities.
They also adapt well to phased development programs.

Another advantage is that these concepts could be designed such that no expendable hardware is needed for either mission. The single-stage-to-orbit vehicles do not appear competitive from any standpoint other than operational simplicity.
This factor, however, could be very important and should keep this class of vehicles under consideration.

From both a weight and sensitivity standpoint, the data indicates that two stage ballistic vehicles. These concepts are the lightest and have a low sensitivity to parametric variation.

 Phased development allows the early use of the crew and cargo system before full development of the booster. Thus, concepts with separate crew vehicles will be more amenable to phased development.
The ability to augment the performance of a stage, once built, is important if the design goals are not met. This augmentation is considered easier with relatively symmetric ballistic boosters.

All the four concepts described are under current study except the two stage ballistic vehicles..."

Space Transportation System analysis
Bellcomm technical memorandum
DATE: July 26, 1971
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