Grumblings of true commercial space travel at NASA

"Explorer" wrote in
oups.com:

Your assumption is that the insurance industry has not yet considered
the issue. Given that companies like SpaceX work closely with insurers
and they plan to send cargo to ISS, what makes you think they don't
have insurance deals lined up already?

Quite simply, because there hasn't been any public noice about it yet.
There *has* been public noise about the difficulties alt.space companies
are having getting insurance for launch and for ground testing, and I
assume that insurance for docking will be no less difficult.

--
JRF

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to prox ops or not for delivering stuff to ISS.

Since the remaining Shuttle flights are limited and fully booked, it is fair
to assume that the ISS will not get any new systems that were not already
planned before shuttle is prematurely retired.

So, some alternative cargo delivery system, wether private, public or
whatever, will need to either have automatic docking capability on russian
ports, or be able to get within grappling distance of the SSRMS and use CBM to
connect to the station.

So station keeping at 1km is not of any use since the station will not have
anything to go and grab it.

In terms of insurance, I feel this would be a non issue. Since the station is
a government owend system (owned by many governments to boot), an incident
would probably be covered by the governments who contracted with the cargo
delivery company who will have undoubtedly signed a contract that liberates it
from any liability should it bump into the station.


The big question is wether the arm outfitted with the hand, would be able to
operate the US Quest airlock from the outside. If so, then Pizza Hut could
deliver pizzas to the vicinity of station, have the arm open the airlock, grab
the pizzas, throw then inside the airlock, close the airlock, and the crew
could then repressurise the airlock and get their fresh pizzas. However,
realistically, a small tug that delivers small parcels on the oustide would
require the station have 2 arms. One to grab the tug, and one to then take
each parcel and move it inside the airlock. But such a system wouldn't require
any docking, just ability to be grappled.

"Tom Cuddihy" wrote in
ups.com:

Jorge R. Frank wrote:
(Henry Spencer) wrote in
:

It also means that the particular station partner is in the critical
path of commercial crew and cargo service to ISS. That's not to say
this is not a viable path, but it does mean that availability of
commercial services prior to 2010 is wishful thinking at best.

People are already thinking in that direction. When Boeing asked
SpaceX for a quote on freight delivery to an orbital fuel depot,
what came back was a quote for delivery to a point 1km from the
depot.

That suggests SpaceX has not thought the problem through. "1 km" is a
meaningless metric, when not tied to a particular relative *velocity*
as well.

They're using standard rendevous terms. 1 km means zero relative
velocity, in the same orbit, 1 km ahead of the spacetug. The space tug
would then perform a manuever to lower its orbit from that of the
target slightly, to catch up to the target, then phase back to the
same orbit within about 200-300 m of the target, after which it's
close enough to be 'driven in' without really worrying too much about
orbital period. (That's how shuttle rdvs happen).

Kinda. :-) Actually, that's a reasonable description of how shuttle deploy-
retrieve RNDZs happen, with the exception that shuttle pilots are taught to
make effective use of orbital mechanics throughout the manual phase. It's
not until about 10 m that they can just "drive in" and more-or-less neglect
orbital mechanics (though the effects are quite visible, even that close).

For shuttle ground-up RNDZs (which is pretty much all of them from now on),
the shuttle enters the phasing orbit from below, rather than from a
stationkeeping point with zero relative velocity. FDOs make it a point of
pride, in fact, to never waste propellant on an orbit-lowering burn during
a ground-up RNDZ.

Of course, then it has to get back to the station, which means
optimally this would all happen behind the station. The tug would then
lower its orbit to catch back up to the station with the payload 'in
hand.' Of course, all the maneuvers have to be done in a short enough
time frame that perterbations don't screw up the parameters, but it's
doable.

The doability depends on the magnitude of the relative velocity error.
Effectively, that error dictates the "retrieval window", both timeline-wise
and propellant-wise, within which the tug must operate. Therefore, if the
relative velocity is not actively controlled, the expected error must be
part of the spec for the tug.

Or at least, that was my naive assumption. :-)

--
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"Henry Spencer" wrote in message
...
In article ,

One obvious solution is to have the tug supplied by one of the station
partners. Then only the tug is an insurance issue, still not trivial
but
vastly more tractable than the station itself.

People are already thinking in that direction. When Boeing asked
SpaceX
for a quote on freight delivery to an orbital fuel depot, what came
back
was a quote for delivery to a point 1km from the depot.

What of a small actively controlled "harpoon" on the end of a kilometre
plus long fishing line? While not as comprehensive as a tug, it might
be somewhat cheaper.

Perhaps it is a technique more suited to retrieving the payloads from
mass launchers.

Pete.

John Doe wrote in :

In terms of insurance, I feel this would be a non issue. Since the
station is a government owend system (owned by many governments to
boot), an incident would probably be covered by the governments who
contracted with the cargo delivery company who will have undoubtedly
signed a contract that liberates it from any liability should it bump
into the station.

Yes, that's called "indemnification", and it's one of the possible
solutions I listed earlier in the thread. The problem is that
indemnification never comes without strings attached, and if history is any
guide, those strings will be intrusive enough so as to negate many of the
advantages of a commercial arrangement. It'll revert to a government-
contractor relationship in all but name.

--
JRF

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"Jorge R. Frank" wrote:

"Explorer" wrote in
roups.com:

How do you maintain a relative velocity of zero, one km from a target,
for an indefinite period of time?

You don't. But you could maintain it for some definite period of time by
stationkeeping. That requires sensors, avionics, and thrusters, which not
coincidentally is the same hardware you need for any other kind of prox
ops.

It seems to me that you could develop any number of cheap/simple
'sensors' that are more than adequate for maintaining station at 1km +
or - an arbitrary fudge factor, yet be utterly unable to perform prox
ops.

D.
--
Touch-twice life. Eat. Drink. Laugh.

-Resolved: To be more temperate in my postings.
Oct 5th, 2004 JDL

"Explorer" wrote:

Its actually enormous news that Boeing is asking an
alt.space company for a quote for cargo delivery to
a non-existant space depot.

Not really. Contrary to popular belief, both the goverment and big
companies deal with small fry all the time.

D.
--
Touch-twice life. Eat. Drink. Laugh.

-Resolved: To be more temperate in my postings.
Oct 5th, 2004 JDL

Jorge R. Frank wrote:
"Tom Cuddihy" wrote in
ups.com:

Jorge R. Frank wrote:
(Henry Spencer) wrote in
:

It also means that the particular station partner is in the critical
path of commercial crew and cargo service to ISS. That's not to say
this is not a viable path, but it does mean that availability of
commercial services prior to 2010 is wishful thinking at best.

People are already thinking in that direction. When Boeing asked
SpaceX for a quote on freight delivery to an orbital fuel depot,
what came back was a quote for delivery to a point 1km from the
depot.

That suggests SpaceX has not thought the problem through. "1 km" is a
meaningless metric, when not tied to a particular relative *velocity*
as well.

They're using standard rendevous terms. 1 km means zero relative
velocity, in the same orbit, 1 km ahead of the spacetug. The space tug
would then perform a manuever to lower its orbit from that of the
target slightly, to catch up to the target, then phase back to the
same orbit within about 200-300 m of the target, after which it's
close enough to be 'driven in' without really worrying too much about
orbital period. (That's how shuttle rdvs happen).

Kinda. :-) Actually, that's a reasonable description of how shuttle deploy-
retrieve RNDZs happen, with the exception that shuttle pilots are taught to
make effective use of orbital mechanics throughout the manual phase. It's
not until about 10 m that they can just "drive in" and more-or-less neglect
orbital mechanics (though the effects are quite visible, even that close).

For shuttle ground-up RNDZs (which is pretty much all of them from now on),
the shuttle enters the phasing orbit from below, rather than from a
stationkeeping point with zero relative velocity. FDOs make it a point of
pride, in fact, to never waste propellant on an orbit-lowering burn during
a ground-up RNDZ.

Of course, then it has to get back to the station, which means
optimally this would all happen behind the station. The tug would then
lower its orbit to catch back up to the station with the payload 'in
hand.' Of course, all the maneuvers have to be done in a short enough
time frame that perterbations don't screw up the parameters, but it's
doable.

The doability depends on the magnitude of the relative velocity error.
Effectively, that error dictates the "retrieval window", both timeline-wise
and propellant-wise, within which the tug must operate. Therefore, if the
relative velocity is not actively controlled, the expected error must be
part of the spec for the tug.

Or at least, that was my naive assumption. :-)

Ok, obviously I'm telling the baker how to bake bread here. Sorry.
My limited knowledge of rendezvous came from a lecture my orbital
mechanics prof, Dr. Chirold Epp gave, but I thought he said you could
generally 'drive it in' within 400m or so--generally any distance you
think you can make up in less than a 1/4th of an orbit. He said he's
been a part of a few rdvs himself, but then again he's been teaching
students for the last 10 years. He's going back to Johnson this year
though--in fact, I think he might already be back there!

Anyway, you never know who you're talkin to on usenet--hope you weren't
offended by my a.s.s.umption.

tom

(Derek Lyons) wrote in
:

"Jorge R. Frank" wrote:

"Explorer" wrote in
groups.com:

How do you maintain a relative velocity of zero, one km from a
target, for an indefinite period of time?

You don't. But you could maintain it for some definite period of time
by stationkeeping. That requires sensors, avionics, and thrusters,
which not coincidentally is the same hardware you need for any other
kind of prox ops.

It seems to me that you could develop any number of cheap/simple
'sensors' that are more than adequate for maintaining station at 1km +
or - an arbitrary fudge factor, yet be utterly unable to perform prox
ops.

True. That would be a big win if the cost of the sensors were a high
percentage of the cost of the overall system. I'm betting that systems
integration, propulsion development, and avionics software development will
dominate the total costs, though.


--
JRF

Reply-to address spam-proofed - to reply by E-mail,
check "Organization" (I am not assimilated) and
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"Tom Cuddihy" wrote in
ups.com:

My limited knowledge of rendezvous came from a lecture my orbital
mechanics prof, Dr. Chirold Epp gave,

Now there's a name I've not heard for a long time. Chirold was a branch
chief in the Flight Design and Dynamics Division back when I was a co-op
student there mumble-something years ago. Legendary man - we all looked up
to him.

but I thought he said you could
generally 'drive it in' within 400m or so--generally any distance you
think you can make up in less than a 1/4th of an orbit.

That was true at the time he left FDDD. Keep in mind, in those days our
shuttle prox ops experience base was all small payloads and you could get
away with quite a bit of brute force. Shuttle-Mir was just gearing up and
Shuttle-ISS was still several years away. ISS is quite fragile and
sensitive to RCS plume impingement. By necessity, prox ops became much more
of a finesse game.

He said he's
been a part of a few rdvs himself, but then again he's been teaching
students for the last 10 years. He's going back to Johnson this year
though--in fact, I think he might already be back there!

Didn't know that. Well, your loss, our gain. I'll have to look him up and
see where he landed.

Anyway, you never know who you're talkin to on usenet-- hope you
weren't offended by my a.s.s.umption.

Not at all - I learned quite a bit in this exchange, thanks!

--
JRF

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