Tuesday, June 12, 2012

Would You Like SLA With That?

Apollo 14 command-service module ("spacecraft")
with attached adapter ("SLA")
being hoisted atop the Staurn V launch vehicle.
Among the many misnomers I hope to discuss in this blog, my nominee for “longest period of lip-service without further consideration” is the Apollo Program’s “Spacecraft-Lunar Module Adapter”, or “SLA” (pronounced “slaw”)[1].

The SLA was the 8.5-m long funnel-shaped structure between the bottom of the 3.9-m diameter Service Module (SM) and the top of the 6.6-m diameter S-IVB final stage of the Saturn IB or Saturn V rocket[2]. It started out serving a simple purpose: providing a rigid connection between the SM and the S-IVB while smoothing the supersonic airflow past them during launch.

Any device which joins two disparate items, whether in plumbing, manufacturing or even electronics, is called an “adapter”, so that part of the name is obvious. In 1962, when the Apollo Program came to include a separate vehicle for landing on the Moon[3], the Lunar Excursion Module (LEM), later shortened to Lunar Module (LM), it became convenient to stow the lander in the adapter for launch. But here is where the misnomer appeared, in two ways.

First, the LEM was a spacecraft, too, just as surely as the unified Command/Service Module (CSM) which was the “spacecraft” in “spacecraft-lunar module adapter”. However, the CSM was designed first, and the LEM was added later, so for a time the CSAM alone was the Apollo “spacecraft”.

Second, the adapter “adapts” between the spacecraft and the launch vehicle, and the LM was simply a Johnny-come-lately passenger hitching a ride in the volume resulting from that structural necessity. Therefore, logically, SLA should stand for “spacecraft-launch vehicle adapter”.

A representative but not exhaustive search of official documentation[4] and press reporting[5] of Apollo developments indicates, surprisingly, that “spacecraft-launch vehicle adapter” was not the term of choice even before the LM appeared, nor was “spacecraft-lunar module adapter” the immediately preferred term thereafter. A 1961 document[6] from the Marshall Space Flight Center (MSFC), which designed the Saturn rocket family, didn’t even refer to the adapter by name, calling it the “Instrument Unit”, which was contained in an adjoining piece of the Saturn structure. Other documents in 1961 to 1963 called it just the “adapter” or “spacecraft adapter”. A change in the approach to lunar landing led to the appearance of the LEM in 1962, so by June 1963, the adapter was called the “S-IVB adapter”, “S-IVB (LEM) adapter” and even the “LEM adapter” within the same NASA documents. In 1964 the press was calling it the “LEM adapter section” and the “Apollo spacecraft adapter” while the NASA documents were referring to it as the “Apollo adapter”, the “Spacecraft S-IVB Adapter” and the “CSM/S-IVB Adapter”. The latter two terms at least had the characteristic of accuracy because they indicated which two components were being adapted.

At the end of 1964, a NASA document referred to the “spacecraft-launch vehicle adapter” and used the abbreviation “SLA” for the first time in print; however, the same document also labeled it the “LEM adapter” in an illustration. In November 1965, a trade journal mentioned the delivery of the first manufactured “Apollo spacecraft/lunar excursion module adapter” and “spacecraft/LEM adapter”. In 1966 the “spacecraft/lunar module adapter” appeared in a NASA press release, while a NASA briefer labeled it as the “Service Module Adapter”—complete with a unique abbreviation, “SMA”, for the first and last time—as well as “SLA” with no expansion. “LM adapter” appeared in a 1967 NASA illustration and “launch vehicle/spacecraft adapter” in a 1968 official report, but by 1969 the familiar “spacecraft-LM adapter” seemed to be dominating[7]. Except for a 1970 contractor document that inexplicably substituted the launch vehicle for the spacecraft, identifying the “Saturn Lunar Adapter” and the “Saturn Lunar Module Adapter”, the now-familiar “spacecraft-lunar module adapter” term has persisted[8].

Other terms in the space lexicon represent similar mindless reptition—here I’m thinking of “crew” to indicate both an individual astronaut and a group of them, and “microgravity” when “weightlessness” is just as appropriate and not guilty of excessive precision—but those are better left to another day and diatribe.


[1] Oral History Transcript, J. Thomas Markley, interviewed by Carol L. Butler, Plymouth, MA, 24 June 1999, for the Johnson Space Center Oral History Project, p. 12-13.
[2] Apollo (spacecraft), http://en.wikipedia.org/wiki/Apollo_%28spacecraft%29 (last checked 11 June 2012).
[3] Apollo lunar module, http://en.wikipedia.org/wiki/Lunar_Module (last checked 12 June 2012).
[4] NASA Technical Reports Server, http://ntrs.nasa.gov, a free repository of NASA and related documentation.
[5] Newspaper Archive, http://newspaperarchive.com, an invaluable subscription-based source for decades of U.S. and foreign newspaper articles.
[6] THE APOLLO "A"/SATURN C-I LAUNCH VEHICLE SYSTEM, MPR-M-SAT-61-5, July 17, 1961 (NASA-TM-X-69174), pp. 130-134ff incl. fig. 6.1 and 6.2. http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19730064291_1973064291.pdf (last checked 4 June 2012).
[7] Williamson, M.L.  and C.W. Fraley, APOLLO 9 SLA PANEL JETTISON SEPARATION AND RECONTACT ANALYSIS, MSC INTERNAL NOTE NO. 69-FM-43, http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19740072593_1974072593.pdf (last checked 3 June 2012).
[8] Duncan, John. “Spacecraft-LM Adapter”, http://www.apollosaturn.com/asnr/SLA.htm (last checked 3 June 2012).

1 comment:

  1. John:

    This question has vexed me for some time, especially since there were occasions when the SLA didn't house an LM. Plus there were plans to put other things in there, including space station modules and manned Venus flyby spacecraft that would have filled the entire SLA volume. And then there were the Wet Workshop plans in which the SLA "petals" would have contained solar cells on their insides.

    For what it's worth, I generally go with Spacecraft Launch Adapter for both the Saturn V and Saturn IB SLA just to keep things simple, since that seems to admit any SLA payload (or none at all). The spacecraft is the CSM and anything inside the SLA is payload.



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