David.Smith%CMU-CS-IUS@sri-unix.UUCP (11/29/83)
Well, if Mohammed can't go to the mountain, then the mountain will just have to come to Mohammed.
katz.uci-750a%Rand-Relay@sri-unix.UUCP (12/06/83)
From: Martin D. Katz <katz.uci-750a@Rand-Relay>
David.Smith@Cmu-Cs-Ius (Dec. 2)
... the breathing oxygen is used for propellant.
The current maneuvering unit does have a number of jets -- for six-axis
control, I believe. I don't know about extra propellant tanks.
In my view, the dangerous possibility is not that a thruster could
become inoperable, but that it could be jammed on, ...
Thank you, I was unaware of the details of the current NASA design of
portable propulsion. I don't think that NASA would have approved the
routine use of breathing oxygen for other purposes a decade ago. Is this
another cost cutting measure?
Suppose that the valve on a jet sticks open, the force can be approximately
counterbalanced by opening the opposite valve. The remaining spin can be
negated by use of the the pair of jets which are 60 degrees from the jet
used to counteract the broken jet. I would worry more about using up all of
that oxygen -- how long before the the pressure runs down too low for the
astronaut to breath or propel himself?David.Smith%CMU-CS-IUS@sri-unix.UUCP (12/06/83)
Whoa!!! I am quoted as having said
... the breathing oxygen is used for propellant.
What I actually said was
OK, but the current unit is in one piece -- which is not to
say that the breathing oxygen is used for propellant.
I don't know what the propellant is, but I can't imagine that it comes
from the breathing supply. My guess is hydrogen peroxide. The little
hand-held maneuvering gun used by Ed White on Gemini 4 had its own
compressed oxygen tank.warner%rand-relay@orca.UUCP (12/06/83)
Yes jets (or thrusters) stuck on is another problem for which a contingency plan must be developed. The idea of throwing objects (such as the jet pack itself) is a bit expensive to say the least. Probably not that effective in any case. As an aside, has there ever been an experiment that would support such a hypothesis that an astronaut could actually perform this feat effectivly ? My original idea of a spring loaded gun shooting a magnet that is connected by a wire to the astronaut seems more direct. Also is there any orbital mechanics that are being over looked? What would be the orbit of an astronaut that had projected himself radially outward from the shuttle? Would he eventually intersect the orbit of the shuttle at a later time? Ken
katz.uci-750a%Rand-Relay@sri-unix.UUCP (12/08/83)
From: Martin D. Katz <katz.uci-750a@Rand-Relay>
...!orca!warner:
The idea of throwing objects (such as the jet pack itself) is a bit
expensive to say the least. Probably not that effective in any case.
As someone mentioned on the net, actually throwing something propel oneself
would be a great feat without a lot of training. I would say that it is an
"If all else fails" alternative. I really only suggested it because it
takes advantage of what is already there. As to expense, in an emergency,
the cost of the propulsion unit is trivial compared to the cost of the
astronaut and suit.
My original idea of a spring loaded gun shooting a magnet that
is connected by a wire to the astronaut seems more direct.
The use of a spring loaded gun is probably a better alternative. Shooting a
magnet and wire might work except that I understand that there is little
exposed ferromagnetic material on the shuttle (even with the cargo bay doors
open), and I understand that an attempt is made to limit the carrying of
magnets on the shuttle because some equipment is sensitive to them. Thus,
there is little place for the magnet to stick. I also think that aiming
might be a problem, and so several shots might be needed (thus, a spring
loaded unit sounds like an advantage). Would there be a problem with the
line tangling between shots?
Maybe instead of a magnet, one could use a wad of very sticky putty. It
might even be an epoxy precurser which would react with the surface of the
tiles (much like some suit patches which have been proposed). As to
tangling, maybe a wrapped fiber which is thin, yet stiff might help.
Also is there any orbital mechanics that are being over looked?
What would be the orbit of an astronaut that had projected himself
radially outward from the shuttle? Would he eventually intersect the
orbit of the shuttle at a later time?
As I understand it, the orbit of an astronaut who projected himself radially
outward from the shuttle would be an ellipse which (because the dV is low) is
approximately that of the original orbit. The actual effect depends on the
direction of the shove, the dV, the original orbit, and the position in the
orbit. Since the dV (change in momentum) is small, in most cases, the
astronaut's orbit would intersect the orbit of the shuttle. Unfortunately,
because the orbits don't match, the shuttle might not be at the intersection
point when the astronaut is. If the difference is small enough, the shuttle
might have moved little enough relative to the intersection point that it
will effectively still be there for the astronaut.
A problem is if the astronaut matches orbit with a satellite in a slightly
different orbit from the shuttle. In this case, he might fall far behind
because if the satellite is in a higher orbit, its orbital period is larger.
In a one orbit EVA, this could be several hundred meters.
As to whether we forgot something in orbital mechanics of throwing or
shooting things -- definitely. Actually, everything in orbit moves
approximately in an ellipse with one focus at the center of the earth. A
propulsion changes which ellipse one follows, and the motion is not straight
line to the astronaut. In fact, I understand that the most efficient way to
move into an orbit further out is to propel oneself tangentially to the
current orbit (speeding up ones motion propels one into a higher orbit).
This is why "retro rockets" work. These effects are not large for an EVA
because the orbits are similar, but the astronaut will need training and
might need some navigational help on a long EVA.eder@ssc-vax.UUCP (Dani Eder) (12/10/83)
9 December 1983
I thought it would be useful at this point in the discussion to
quote from the Flight Data File, which is the set of data the astronauts
carry with them and the Houston folk refer to. One volume is the "Crew
Activity Plan", which details the timelines for the crew. The particular
one I am looking at is for STS-13, which includes the Solar Maximum Repair
Mission.
[Section 7: Notes, page 7-8]
G. PAYLOADS
1. LDEF (Long Duration Exposure Facility)
. . .
2. SMRM (Solar Maximum Repair Mission)
The SMRM includes the SMM observatory presently in orbit and the
Flight Support System (FSS) for berthing the SMM and return of the SMM
to the ground if it cannot be repaired in orbit.
The STS will launch from KSC and will rendezvous with the SMM
observatory. . . .
Retrieval and repair of the SMM will be made using the Remote
Manipulator System (RMS) in conjunction with Extravehicular Activity (EVA)
which includes the Manned Maneuvering Unit (MMU) operations. The first
of two scheduled EVA's starts with the Orbiter stationkeeping near the
SMM. The MMU crewman will fly over to the SMM, attach to one of its
trunnion pins, and null the SMM rates ((comment: that means stopping any
spin)). The orbiter will then close, and the SMM will be grappled by
the RMS and berthed on the FSS. After berthing, the SMM is powered down
and the MACS module ((the broken part)) is replaced. . . .
Dani Eder
Boeing Aerospace
ssc-vax!ederREM%MIT-MC@sri-unix.UUCP (12/10/83)
From: Robert Elton Maas <REM @ MIT-MC> The standard technique on Earth for tossing a weight on a string and reeling it back in repeatedly until you catch ahold of what you're trying for, is a fishing pole. In space you'd spin momentarily while casting, but mostly stop spinning as soon as you reached the end of the swing. The only residual spinning would be due to the sinker and hook (the part that actually kept moving). In space probably the pole wouldn't be needed, a simple reel held in your hand would get enough momentum to make the tackle drift across to your spacefish (the STSh orbiter). Perhaps we should suggest somebody actually experiment with this device on some upcoming flight?