Mdthbs

The Apollo missions were in communications blackout when the spacecraft's orbit took it to the far side of the Moon. During the missions, the craft had to perform maneuvers such as the lunar orbit insertion burn on the far side. Without ground support, and without any way of even telling the ground what went wrong, if something did. That seems like an unnecessary risk to me!

I see no reason why NASA couldn't have used relay satellites to allow communications on the far side. Multiple lunar orbiters predated the manned missions, and relay satellites had been operational in Earth orbit since 1962. The cost of such relays would surely have been quite small compared to the whole project.

Was this considered at some point? If so, why wasn't it done?

It's not mentioned in Apollo documentation. However, these would be the arguments against it:

1. 
   

   The idea of two spacecraft was already controversial. Now you want three? The original Apollo concept was a "direct" mission. The entire mission would launch as one vehicle, shedding pieces as you go, but never putting pieces back together. All of the astronauts and their Earth return vehicle would land together on the moon and take off again.

   
   
   

   Apollo ended up using "lunar orbit rendezvous" instead. One vehicle would launch toward the moon. However, once in lunar orbit, a minimal lander would separate from the main vehicle, land on the moon, and return back to lunar orbit to dock with the main vehicle.

   
   
   

   All of the major domos at NASA (e.g. Von Braun, Faget, Gilruth) were initially opposed to the idea of LOR. Rendezvous had never been done before. It needed new mathematical models, automated flight computers, miniaturized radar, docking mechanisms, more stations in mission control, crew and mission control training, and so on. It was only when the size and price of a direct mission was determined to be too costly that the LOR approach was taken seriously. And it had to be proven reliable in the Gemini program.

   
   
   

   Now, you want three (or even more) spacecraft? The battle for just two was bad enough, no one wanted to pick that fight again.

   
   



2. Satellites were unreliable. The technology was new, and their lifespan was short. When a satellite died, there was no way to fix it, so now you must deal without it. The long-term effects of radiation, thermal degradation, and micrometeoroids were not known until the Pegasus satellites were launched on the Saturn I test missions AS-103 through AS-105.




3. The technology was unproven. Communication had only been done between ground and spacecraft. Now you want both ground-to-spacecraft and spacecraft-to-spacecraft? The latter hadn't even been done yet!




4. We were in a race. It's not that the above issues were impossible, but they would take time to get them to work. (For example, we can do it today.) We were in a race with the Soviets, and in a race with the end of the decade. There wasn't time to develop a solution.



5. 
   

   You ought to plan for that contingency anyway. One of the most serious problems with spaceflight is losing communication with mission control. But it is also something you can plan for. You train your astronauts how to diagnose the problem, how to solve the problem, and how to stay safe in the meantime. You are going to plan for that contingency anyway, so why not embrace it?

   
   
   

   Also, going around the far side of the moon is a predictable, regular event. You can make your plans around this schedule. And the LM lands on the near side of the moon, so you don't have to worry about that.

   
   

A communications satellite would have to be in a halo orbit around the Earth-Moon L2 point to have continuous, simultaneous visibility of both the Moon's far side and Earth. The first paper describing this kind of orbit was written in 1968, too late to be used for Apollo.

• P. E. Schmid, June 1968: Lunar Far-Side Communicatio Satellites; NASA TN D-4509
  

This was followed up by

• Robert Farquhar, 1971: The Utilization of Halo Orbits in Advanced Lunar Operations; NASA TN 0-6365
  

I can't reach the NTRS right now, but it should have more data on this subject. More tomorrow.

SUMMARY

This report investigates the feasibility of communicating with Apollo spacecraft behind the moon and of communications between two such spacecraft. Two satellite geometries are considered for signal relay: a libration or "Hummingbird" satellite anchored 65,000 km behind the moon and a lunar-orbiting relay satellite at 1000-km altitude. The signal transmission frequencies of the Apollo spacecraft are VHF and unified S-band (USB) operating at 300 MHz and 2 GHz, respectively. The three propagation links examined in this report include: lunar far side, i.e., Lunar Module (LM) on lunar surface and/or lunar-orbiting command and service module (CSM), to earth; lunar far side LM to CSM; lunar far side surface to surface.

It is shown that as a result of antenna pointing constraints, only the libration or "Hummingbird" satellite is suitable for relaying USB tracking and communication data to earth. It is also shown that acquisition of a 1000-km altitude lunar satellite by an Apollo spacecraft dictates the use of VHF. Various modes-feasible and unfeasible-of lunar far- side radio relays are listed below, with their respective methods of communication.