Dextre Robot used on the International Space Station is a step in the right direction.
What form would a future EVA-RPV (or Astrobot) take? Possibly there will be several types, but the form I tend to imagine looks a little like a spider.
There is a central body of roughly spherical shape, perhaps half a metre in diameter. From the equator of the sphere sprout four long spindly limbs. I choose to term these limbs since they are both locomotory and manipulative in function. Using these limbs the Astrobot can push off from surfaces and fly without expending propellant. The limbs also act as shock absorbers for a soft landing when it reaches another solid surface. Equipped with prehensile claws, the limbs can be used to hang onto handholds, move about the surface of a satellite or spacecraft and handle tools or objects of interest. Shorter arms mounting specialized tools are also mounted here.
The upper hemisphere of the body features several exhaust ports angled in a variety of directions. This is the Astrobot's gas propulsion system and by firing the ports in various combinations it can propel itself in any direction.
The lower hemisphere of the body mounts the majority of Astrobot's primary sensor systems. Perhaps there is a transparent shield to protect these, making the Astrobot look a little like it is wearing a space helmet. Like the spider it resembles, the Astrobot has multiple eyes. A pair of high definition cameras provides the operator with stereoscopic vision. Provision is included to magnify small objects such as printed circuit boards. Infra-red and Ultra-violet sensitive cameras are also included to provide additional information. In addition to these passive sensor systems the Astrobot has a Laser rangefinder and Scanning LIDAR system. There is also a bank of illumination LEDs so the operator can see into dark places. Video pick-ups positioned on the limbs or other parts of the body give the operator alternate views and greater situational awareness.
Continuing the spider analogy, the Astrobot can also deploy lines to haul itself towards an object, haul objects towards it or tow items.
Astrobot's environmental system requirements will be fairly basic. Some of its component systems may not function well in extremes of temperature or radiation so may need cooling, shielding or heating but most of its systems have been designed to work in airless vacuum.
While an Astrobot can be operated by a single person the feed from its sensors can be shared between multiple observers. For example, when repairing a satellite a whole team of engineers can see what the operator sees, offer advice or can take over control if warranted. The use of telefactoring technologies such as Waldos allow the operator to work on the task at hand as if he was actually there.
Some jobs such as orbital construction may require teams of Astrobots working together. To facilitate this process each Astrobot will be given an individual colour scheme and identification lights.
While the Astrobot can perform many forms of orbital labour that previously required a human in a spacesuit, there is an obvious question of how to get the Astrobots into orbit in the first place.
One solution would be to carry Astrobots in existing spacecraft such as the Space Shuttle Orbiter. On the plus side this would allow the Shuttle crew to complete many of their missions without ever having to suit-up. It also means that Astronauts are available to EVA should there be any situations that the Astrobot cannot deal with. On the downside, a Shuttle is a very inefficient way to get an Astrobot into space. Because it carries a human crew the shuttle must carry environmental systems, food, water, toilet facilities and a whole host of other items which increase the size and weight of the spacecraft.
An advantage of using Astrobots is that not only does the operator not need to use a spacesuit, but that they don't have to actually be in orbit. The Astrobot is remote controlled so as long as there is a good signal and time delay is not an issue the operator can be any distance from his Astrobot. Most manned EVAs from Shuttles are at 115-400 miles altitude, so time delay from a radio signal will not be an issue if Astrobots are used at this altitude. One can repair a satellite sitting safely on earth, sipping a cup of coffee.
Geostationary satellites in the Clark Belt are at 22,300 miles altitude, which I calculate as a time lag of around a quarter of a second for a command to be get there and the results viewed. I don't know if such a delay would be significant to Astrobot operations and much may depend on the software and the Astrobot's ability to perform pre-programmed subroutines. In other words, rather than controlling every movement of the Astrobot the operator will in many instances just issue the command Cut there or Solder that and let the subroutine do the rest. Geostationary satellites are currently out of reach of our manned spacecraft so you may wonder why I am considering the operation of Astrobots at such ranges. My reasons will become clear later on.
Since an Astrobot controller can stay on Earth, the problem boils down to getting the Astrobot into orbit. An Astrobot doesn't need air, pressure, water or food and isn't bothered about being cramped or not having a window to look out of. Some protection against the temperatures of re-entry may or may not be needed, although such measures are likely to be fairly simple. What this means is that Astrobot can be put into orbit by a much smaller and simpler spacecraft than the Shuttle. What form would such a spacecraft take? We can look to the past to get a few ideas.
In the mid-80s DARPA proposed an unpressurised one-man space vehicle with the rather grand title of the Space Cruiser, and sometimes rather misleadingly referred to as a Space Plane. Supposedly one application of this craft was as a Space Fighter to shoot down enemy satellites. Since unmanned missiles can do that job a more practical application was to take an astronaut for satellite inspection or repair. Quite possibly the satellite being examined or modified may not have belonged to America!
The Space Cruiser was based on a Hypersonic Cone configuration that had been used for Poseidon MIRV warheads. It was about 56-60 wide and 25-30 feet long. Small strakes or fins would have provided aerodynamic control in atmosphere. It was either circular in cross section (for easy construction) or elliptical (for better aerodynamics). The spacesuited pilot(s) sat near the back, just ahead of the main engine, which would have been of Aerospike configuration both for compactness and its altitude compensating tendencies. By using a ring of sixteen to twenty individual nozzles thrust could be vectored for manoeuvring in space.
Most diagrams of the Space Cruiser do not show the aerodynamic control surfaces nor the Attitude Control Systems (ACS). The illustration right was probably not the final configuration selected but does show the basic layout and several features not included in other diagrams. Note that the forward section of the cone apparently swings down while the Space Cruiser is in orbit, exposing the sensor systems and the forward ACS thrusters. The forward part of the cone also contains a payload area, which is easily accessible with the cone swung down. It seems likely this payload bay would also have contained the armament if the Space fighter application is true. It has also been suggested that payload could be carried behind the plug within the engine ring.
The basic configuration of the DARPA Space Cruiser is a good start for an Astrobot delivery system. We will call this new variant the Coneship, although I have a preference for Pinnacle. By eliminating the pilot, his chair and environmental system and replacing it with automated guidance we save a significant weight and free up internal volume. The vehicle could carry several Astrobots, either in the rear area and/or in the forward payload space. The increased capacity can also be used to carry additional fuel, allowing the vehicle to reach higher altitudes. Since an Astrobot can be fitted into a smaller space than a human it is also possible that a much smaller Coneship could be used, perhaps of no more than a metre in diameter. The resultant savings in weight could be used to increase performance or reduce running costs.
Putting an Astrobot in orbit to repair a satellite is a considerably cheaper option than sending a man.
A variety of launch systems were proposed for the Space Cruiser. It could be launched by submarine or land based ICBM, or a variety of other booster rockets. Another proposal was that up to eight could be carried in the cargo bay of a shuttle. Presumably Space cruisers deployed from a shuttle could be used to reach satellites above the shuttle's effective altitude. The option that most interests me is that the Space Cruiser could reach orbit if launched from a high flying conventional aircraft such as a modified 747 or a B52. It may be possible to launch the smaller varieties of Astrobot carrying Coneship from smaller aircraft. Whereas a 747 usually has a maximum ceiling of around 40,000ft and a B52 50,000ft fighter aircraft such as the obsolescent F-15 can achieve 60,000ft, the stripped Streak Eagle achieving 103,000ft. Launching from an aircraft first stage was also the system used for the private venture space vessel SpaceShipOne, of course.
The maximum altitude/range of the Space Cruiser would have doubtlessly depended on the form of first stage used.
Another option for getting Astrobots into orbit is some form of SSTO (Single Stage To Orbit) rocket. A lot of the ground work has been done for these systems. Rockets such as SASSTO and Phoenix used an Aerospike configuration while Delta Clipper (DC-X, DC-YA, DC-Y) used more conventional rockets. Several companies such as Armadilo Aerospace and Blue Origins have continued to develop these ideas. Their vehicles are intended to transport humans and it is obvious that SSTOs built to deploy Astrobots would be smaller, simpler and cheaper.
An SSTO of Space Cruiser dimensions and configuration for deploying Astrobots is probably possible. Such a space vessel would be designed to be versatile. For low earth orbit missions it could get into orbit under its own power. For higher altitude mission boosters could be added, a carrier aircraft used or the vessel could be carried into orbit by a Shuttle or larger SSTO.
Once an Astrobot Carrier is in orbit it can be steered towards the satellite or area of interest. The Astrobot or Astrobots would EVA and get on with the intended task. Astrobots can work nearly constantly. They never tire or run low on air and controlling operators can work in shifts. Occasionally they might need to return to their space vehicle to replace a depleted battery with a recharged one or to top up their propulsion tanks.
Once the Astrobots have completed their task there are several options. The Space Cruiser and SSTO designs already mentioned were designed to be reusable space craft. On many designs the truncated cone/plug of the aerospike engine was also intended to act as the heat shield during re-entry. As one might expect from its MIRV inspired shape, the Space Cruiser was intended to re-enter the atmosphere point first. It is quite possible that our Astrobot carrier will return to Earth, its crew of Astrobots ready to be overhauled and readied for another mission. If the original mission was the recovery of a satellite or space probe it is obvious that the safe return of the Astrobot Carrier is an essential part of the mission. On the other hand, it might be decided there is no hurry to bring the Astrobots back home. Unlike Astronauts, the Astrobots are not going to run out of food, air or water or get bored. Why not keep them in orbit a while in case of the eventuality that another mission might be arise? In space the Astrobots are protected from corrosion and many of the other factors that limit the lifespan of machines on Earth. All they need is power, and this can be easily provided if their carrier vessel can deploy a solar panel. If they run out of reaction mass for their propulsive systems they can still use their line launchers or use their limbs to propel themselves between solid objects.
It may be decided that recovering Astrobots is not economic in some circumstances. Simply place them in orbit and use them until the job is done or they are worn out. For very high altitude satellites nearly all of the carrier vessel's fuel might be used to reach them and return may not be practical. Perhaps after sending Astrobots 23,000 miles for a repair it is considered prudent to keep them in the neighbourhood in the event further action is needed. The Astrobots wait on standby, perhaps for years until they are needed again. If this strategy is favoured we may see one-way variants of Astrobot Carrying Coneships and SSTOs. These would carry less fuel and lack return-trip equipment such as heat shields, landing gear and parachutes.
There is a third strategy for deploying Astrobots, and that is to deploy them with the satellite in the first place. In future, each high value satellite launch might include a pair of Astrobot caretakers. Already in place, they can be activated to conduct any routine or emergency tasks that may be needed.
It will not just be in maintenance that telepresence and robots will have applications, but also in space exploration. In his insightful article from 1992 Bruce Sterling suggests:-
Advances in computers and communications now make it possible to speculate on the future of "space exploration" along entirely novel lines. Let us now imagine that Mars is under thorough exploration, sometime in the first quarter of the twenty-first century. However, there is no "Martian colony." There are no three-stage rockets, no pressure-domes, no tractor-trailers, no human settlers.
Instead, there are hundreds of insect-sized robots, every one of them equipped not merely with "true television," but something much more advanced. They are equipped for *telepresence.* A human operator can see what they see, hear what they hear, even guide them about at will (granted, of course, that there is a steep transmission lag). These micro-rovers, crammed with cheap microchips and laser photo-optics, are so exquisitely monitored that one can actually *feel* the Martian grit beneath their little scuttling claws. Piloting one of these babies down the Valles Marineris, or perhaps some unknown cranny of the Moon -- now *that* really feels like "exploration." If they were cheap enough, you could dune-buggy them.
No one lives in space stations, in this scenario. Instead, our entire solar system is saturated with cheap monitoring devices. There are no "rockets" any more. Most of these robot surrogates weigh less than a kilogram. They are fired into orbit by small rail-guns mounted on high-flying aircraft. Or perhaps they're launched by laser-ignition: ground-based heat-beams that focus on small reaction-chambers and provide their thrust. They might even be literally shot into orbit by Jules Vernian "space guns" that use the intriguing, dirt-cheap technology of Gerald Bull's Iraqi "super-cannon." This wacky but promising technique would be utterly impractical for launching human beings, since the acceleration g-load would shatter every bone in their bodies; but these little machines are *tough.*
Not sure how an airframe will manage the recoil of a railgun, but the general concept of small explorer robots is sound. Sterling describes them as insects but in fact a whole variety of forms may be needed. Small airships, micro-submarines and many forms between. A common workhorse might resemble a cross between a scarab beetle and a First Wold War tank. What it cannot craw over it may be light enough to hop over using a piston or flipper.
Returning to my original theme smaller robots may also have applications in maintenance. Some things will be more easily dealt with by several “repair-roaches” than larger astrobots, or the two forms work together in unison.