al@ames.UUCP (Al Globus) (10/10/84)
Unfortunately I lost the original article so I can't quote it here. The premise is a nice idea, it combines the concept of teleoperators and tethers to do work in space - or at least move from place to place. There was some fuzzy thinking, however, that I'd like to address: The cost estimate was a few tens of millions. Unfortunately, a single shuttle launch is about $150 million. Also, don't underestimate the difficulty of designing hardware that works in the extreme thermal environment of low Earth orbit. Power in low Earth orbit is not easy to come by. First of all you lose sunlight for almost half the time and must run on batteries. Second, the solar array gets big as the power goes up and you have control problems and orbit maintenance problems requiring frequent reboost because of atmospheric drag (the atmosphere doesn't disapear at 100 miles, it just gets progressively thinner). As a reference point, the reference space station has 75 Kwatts continuous power. 25 for housekeeping and 50 for payloads. Teleoperation from Earth stations to low Earth orbit is not straight forward. Communciation direct from a ground station is limited to a few minutes per orbit (one orbit is about 90 minutes) so continuous communication must go through geosynchronous satellites which introduce a delay of up to a half a second round trip. Also, the tv signals needed for detailed work consume a lot of bandwidth. An automated space station cannot meet all space station goals. One of the prime space station requirement is for life science research. There is no robot in hand or in sight that can inject a rat, much less deal with unexpected problems. This brings us to the real need for people in orbit. It is not necessarily true that an automated station can meet space station requirements more cheaply than a manned station. Machinery, particularly payloads, must be much more fault tolerant when no repairman is available. No machine can match the hand-eye-brain capabilities of the average person, not by several orders of magnitude. This ability gives the designer enormous flexibility and automatic fault tolerance (people can fix the equipement). Also, debugging equipment, a major space station requrement, is extremely difficult when you're hundreds or thousands of miles away. In any case three major space station requirements are difficult or impossible without people: life science research, materials processing research and development, and payload refurbishment and repair. The cost of man is not as high as one might think, particularly since life support must be supplied for experimental animals and plants in any case. Orbital operations are not nearly as critical as launch and landing, so the safety problems are not as severe or as expensive. As noted above, most of the power (and therefor cooling) is associated with payloads not systems (which includes life support). Guidance, navigation, and control are essentially unaffected. Autonomy is enormously increased leading to fewer ground controller, etc. An accurate study would be expensive, but I wouldn't be surprised if a manned space station is CHEAPER than an unmanned station for the space station missions as they stand today.