The Space Reviewin association with SpaceNews

Apollo in Earth orbit
Illustration of an Apollo spacecraft approaching the docking adaptor used for ASTP. Will a direct descendant of Apollo perform similar docking with the International Space Station? (credit: NASA)

Orbital Space Plane: Back to Apollo?

<< page 1: introduction

The basic concept the study presented was a CRV/CTV similar in size and design to the Apollo CM. While the CM was designed to carry only three people, one short of the OSP Level One requirements, the report noted that studies for the Skylab program showed that the CM could be modified to carry up to five people. Scaling up the size of the CM by five to eight percent, the study noted, could make the capsule large enough to accommodate six or seven people, enough to handle the projected future capacity of the ISS.

Beyond the general shape of the capsule, however, the report reveals that little else from the Apollo CM would be retained. The structure of the capsule would be modified so it could handle the 105 kilopascal (15 psi) air pressure used in the ISS today, rather than the 34 kPa (5 psi) pure oxygen environment that Apollo used. The CM’s original guidance, navigation, and control systems, as well as cockpit displays, would be replaced by “entirely new electronic systems and displays,” according to the report. The vehicle will also require “100% new software.” Power will be provided by “state of the art” batteries rather than Apollo-era fuel cells.

Beyond the general shape of the capsule, however, the report reveals that little else from the Apollo CM would be retained.

The spacecraft will also require the means to deorbit. The study proposes developing a separate deorbit propulsion module for the CRV that would be based on Apollo Service Module’s (SM) engine or the propulsion system Aerojet developed for the cancelled X-38 CRV prototype. (The CTV version of the spacecraft would require a modern version of the SM itself.) The capsule will need a new thermal protection system, as the phenolic epoxy resin ablator that was used for Apollo is no longer manufactured. The report recommends using “much improved” ablators that have since been developed but would need to be qualified for human spaceflight.

The report also addressed the matter of landing the spacecraft. Apollo capsules, of course, splashed down in the ocean in predefined locations, and were recovered by a network of helicopters and ships. This is more difficult to accomplish for an Apollo-derived CRV, which could be called upon to depart the station and deorbit on a few hours’ notice. The infrastructure required to continuously staff a large number of landing sites worldwide—which may be required to meet the 24-hour medical care deadline spelled out in the Level One requirements—would likely be cost-prohibitive. The Apollo CM also had a very modest cross-range capability of about 30 kilometers, but was accurate to within 1.6 kilometers. A complicating factor in choosing reentry sites is the CRV’s deorbit propulsion module, which would also reenter to the west of the CRV itself.

The recent Soyuz TMA-1 landing, nearly 500 km off-target, may raise questions about capsule landings in general.

The report recommends that water landing sites be chosen on western shores of landmasses or near islands, close enough to allow land-based recovery crews to meet the spacecraft while allowing the propulsion module to fall harmlessly at sea. The report also looked at land recovery options, ranging from air bags to parafoils to Soyuz-type retrorockets, but also concluded that any landing sites would have to be on islands or western portions of landmasses because of the propulsion module reentry. It’s likely that capsule reentry of any kind will be closely studied after this weekend’s Soyuz TMA-1 landing, where an unspecified problem caused the capsule to land nearly 500 kilometers short of its landing site, delaying recovery of the crew by several hours.

In the end, the report makes it clear that an “Apollo-derived” CRV or CTV will place far more of an emphasis on “derived” than on “Apollo”. Other than the generic shape of the capsule and a few minor subsystems, very little of the original Apollo design was deemed suitable for a future design. This should put the brakes on speculation that all NASA needs to do to build a new capsule is to simply dust off the old Apollo design.

NASA and its industry partners will likely study the capsule concept, either heavily derived from Apollo or entirely new designs, in the months to come. There is no guarantee that a capsule design will be selected or even deemed suitable: all NASA needs to do to effectively rule out a capsule is to add a high cross-range requirement that any capsule design would be hard-pressed to meet. What this report shows is that a capsule design for a CRV or CTV is feasible and potentially less expensive than a winged design. It also shows, though, that it will be harder than simply rebuilding Apollo.