Re: DART nearly a bullseye

<Reference at bottom>

lol, sorry, I don't know Rube Goldberg, but employing hundreds of
engineers in multiple states and field centers is usually a big plus at
NASA budget meetings. Thanks, for the input, it makes the idea more
palatable for NASA.

But, really, Tethered Capture is really just the start, and a reasonable
one at that. The Tether and Hook, really can fly off in any direction. 180
degrees of a sphere originating at it's attachment point. If it were to be
kept ready, it could easily be used to go get anything that has fallen off
the Space Station, as long as whatever it is, is still in close proximity.
With reasonable software it could be commanded remotely from the ground,
inside the station or possibly a space walking astronaut. Even during
space walks it could be used to rescue a stranded astronaut, or some tool
or part that he dropped and just can't quite reach. But, that might
require strategic placement of several of them around the space station.

Continuing with some of the follow on projects, one of the more
interesting is using a much longer and stronger version of the Tether and
Hook to deorbit all visiting space craft. I think this has been discussed
before on this group. Just lower the Shuttle, until it's velocity (same as
the Space Stations) and altitude (quite a bit lower that the Space
Stations) meet the Shuttle deorbit targets. All that is left is to drop
the Shuttle at the right time to land on it's intended runway. This whole
concept is nice, because the Shuttle and all other visiting space craft
would no longer need to carry fuel to deorbit. Plus the Space Station gets
all the energy that would have been used to deorbit the Shuttle. The Space
Stations Orbit is raised by quite a bit. Essentially, it saves all the
deorbit fuel for the returning space craft, and adds delta V to the Space
Station equivalent to the deorbit fuel. A double bonus. In reality, a
single bonus for manned vehicles, as they would require contingency
deorbit fuel.

Who is Rube Goldberg?

As far as crit-1 failure modes I'm having trouble of coming up with just
one. But, maybe you can help me out, what crit-1 items were you thinking
of? If the cable breaks, that's just a missed capture, use a backup cable.
Just be careful not to aim the Hook at the arriving vehicle during the
cast, wait until the Hook is really close to the vehicle. Then with the
low thrust there isn't enough distance between the two to build up any
momentum if the cable were to break. Since the Shuttle is in a circular
orbit around the Space Station, the approach of the Hook is never aimed at
the Shuttle, until the Shuttle flies across the R-Bar, which is when it
would be time to let some line out and move the last 30 feet to the
capture plate.

I would hope you already know that approaching from the R-Bar is a safe
separation approach, meaning, stop thrusting or the line tension stops and
the orbital mechanics of the situation will safely separate the two
vehicles.

How many crit-1 items are there currently in close proximity ops and
docking? I can think of one crit-1 item that it would eliminate. An RCS
Jet stuck "on" in close proximity to the space station. Since orbital
mechanics are trying to separate the Shuttle and the Station during an
R-bar approach, the Shuttle must constantly thrust towards the Space
Station. If the RCS jets were to get stuck "on", it wouldn't be long
before the Shuttle would slam into the Space Station. By the time the crew
assessed the situation and attempted to do anything about it, it would
already be too late. Even a small velocity impact of two massive vehicles
will cause massive damage. Possibly disabling the Shuttle and making the
Space Station useless as a safehaven. This is true for every vehicle with
an R-bar approach.

And if you think an RCS jet can't get stuck "on", just ask the commander
of STS-114. She had an RCS jet get stuck "on" during a critical portion of
a TAL a simulation. It was a valid problem with the onboard flight
software, not a simulation funny. The problem had been there for many
years, it just had not manifested itself before.

New MPSR positions? I think your missing the point of one of the major
selling points. It moves Proximity Ops and docking out of the realm of the
arriving vehicle, and under direct control of the Space Station. It gets
rid of the Shuttle proximity ops people, the Russian proximity ops people,
the European proximity ops people, Chinese..., and replaces them with one
group of proximity ops people working for the Space Station. A big
improvement in safety and cost.

As far as implementation before the Shuttle program ends, you have to
start somewhere. The Shuttle is history, but it's replacement isn't, and
any other new vehicle capable of going to the Space Station. Tethered
Capture eliminates the Proximity Ops requirements for every future vehicle
that is designed to visit the Space Station.

An example of this might be an unmanned Space Station module delivery,
launched on an expendable booster. Just attach a small control module to
one end of a huge Space Station module. It doesn't need thrusters at both
ends of the cargo, just one end. This gives the small control module and
much larger cargo enough attitude control, rotational (3-axis) and
translational (1-axis, actually more like 1.2 instead of 1), to meet the
Capture Requirements. The small, compact delivery control module could be
reused, sending things up to higher orbits, or brought back to earth to
deliver another module. The Shuttle would no longer be required to deliver
modules. A delivery module is probably going to have to be developed at
some time in the future, after the Shuttle is retired. Mars missions or
yet to be built Station modules. Eliminating Proximity ops as a
requirement simplifies the delivery module's design.

Proximity ops and docking is a much harder problem. Thrusters are required
at both ends of the cargo to give a full 6-axis precision control. Look at
what happened to the DART.

"Convoluted", I would have chosen the terms "simple" and "elegant". A
highly maneuverable, light weight, single engine tethered hook with
precision control in all six-axis. When is the last time you heard of
such a space vehicle, six-axis control, "one" engine? Who would have
thought it was even possible? I kind of like it.

Anybody want to hear a story about how the idea came about?

--
Craig Fink
Courtesy E-Mail Welcome @ WeBeGood@xxxxxxxxx





On Tue, 19 Apr 2005 01:30:38 +0000, Jorge R. Frank wrote:

> Craig Fink <WeBeGood@xxxxxxxxx> wrote in
> news:pan.2005.04.18.16.58.24.54623@xxxxxxxxx:
>
>> Video cameras, range finders, radio control, add a computer with all
>> the nice bells and whistles. Hook propellant recharging, battery
>> recharging. Redundancy, a couple of extra fishing rods (Reel, Line and
>> Hook). Emergency cable cutters. Now it's finally beginning to sound
>> like a project NASA could love.
>
> You got that right. It's a convoluted, Rube Goldberg-esque tech-fetish
> solution that will cost a bundle, keep hundreds of engineers busy at
> multiple field centers, and if you're lucky it will only introduce as many
> crit-1 failure modes as it solves, and just might be ready for flight test
> by the time the shuttle fleet retires. The six-axis maneuvering hook at the
> end of the tether was a nice crowning touch; I figure that's worth at least
> three new MPSR positions to support the RNDZ GPO (if STS-46 and 75 are any
> indication).
>
>> Need some pictures to go with this long winded description?
>
> No, the picture's quite clear already. Thanks!

--
Craig Fink
Courtesy E-Mail Welcome @ WeBeGood@xxxxxxxxx
.

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