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Amadeus
2005-Jan-17, 02:05 PM
Stop me if this si a stupid question but it seems to me that weight is an issue when planning probe missions.

My question is why dont we start making probes sectional so we can assemble them in orbit like the ISS? That way we could build larger probes plus because we could send up fuel as well could we not make them travel faster because they will have the ability to have more burn time in space.

The other advantage is that if a rocket explodes on the pad the whole mission is not lost just that part of it that was being sent up at the time.

Of course this will increase the cost of the mission with multiple trips.
(theres no such thing as a free launch) :D

But in the future we'll have the space elevator to take are of things.

kucharek
2005-Jan-17, 02:27 PM
I guess, the only advantage would be in saved structural weight. Currently, a probe has to survive a launch in assembled state. Several Gs, noise, vibration.
If we can push them out of earth orbit with a low-thrust engine, we could assemble delicate parts shipped in containers into orbit in a much less rigid structure, thus saving weight.
But if you look at how probes are assemled and tested and checked and tested and under which conditions, it is hard to imagine how this could be done in a current space station. Currently the costs would be so much higher for the new infrastructure, that it never would pay.

Amadeus
2005-Jan-17, 02:46 PM
I was thinking more of a Modular system where the astronaught just has to bolt the pieces together. I would not like to be doing soldering in Zero G :o

Can this not be done on the ISS now?

Think of it as what would happen if Ikea made space probes.

The other advantage I can see is that the system can be fully tested after it has gone through the stress of launch. I expect this can be done now but we cannot do anything about it at this stage except for software changes.

ToSeek
2005-Jan-17, 02:51 PM
Installing a full spacecraft integration and test facility in orbit, which would have to include cleanrooms, thermal vacuum test chambers, vibration test chambers, etc., would not seem to be practical.

kucharek
2005-Jan-17, 02:54 PM
I was thinking more of a Modular system where the astronaught just has to bolt the pieces together. I would not like to be doing soldering in Zero G :o

Me too. :-)

Swift
2005-Jan-17, 03:03 PM
Installing a full spacecraft integration and test facility in orbit, which would have to include cleanrooms, thermal vacuum test chambers, vibration test chambers, etc., would not seem to be practical.
But what about a generic probe platform, that could be configured differently for different missions. Sort of like Hubble with its swap out instruments. Almost all the missions have guidence, communications, power, data acquisition, propulsion, stabilization, instrumentation. Whether you assembled it on the ground or in orbit, could such a system save time/money on development?

Nicolas
2005-Jan-17, 03:15 PM
Mission design uses of the shelf technology to save money and development time. GPS position control is a good example. Of course, this is ground built technology. So apart from the "already in orbit" thing (so savings on launch weight) there is no real advantage. Besides, the support system would have to return everytime (if you went to pluto with your probe, and you want to use the support system of that probe to go to Venus...)

Kizarvexis
2005-Jan-17, 03:25 PM
I would guess it is because so far every probe could be built to fit into a single launch. Amadeus, are you wondering why we don't send a modular probe so that a whole bunch on instruments could be sent at once instead of multiple missions?

Kizarvexis

Amadeus
2005-Jan-17, 03:49 PM
I would guess it is because so far every probe could be built to fit into a single launch. Amadeus, are you wondering why we don't send a modular probe so that a whole bunch on instruments could be sent at once instead of multiple missions?

Kizarvexis

I was just thinking that because it seems to me that the biggest limiting factor has been weight why don't we use a mulitple launch system to send modular parts to a station (say a modified ISS ) use that as a platform for assembly and launch we could have our "wish list" included plus the probe could be as big as we want.


[EDIT] I have just thought of someting. If the probe capacity is large then we can have more instrements aboard. This could help with funding because a country that does not have it's own space program could just buy space on the probe.

papageno
2005-Jan-17, 04:10 PM
I have just thought of someting. If the probe capacity is large then we can have more instrements aboard. This could help with funding because a country that does not have it's own space program could just buy space on the probe.
Don't they do this already?

Amadeus
2005-Jan-17, 04:23 PM
I have just thought of someting. If the probe capacity is large then we can have more instrements aboard. This could help with funding because a country that does not have it's own space program could just buy space on the probe.
Don't they do this already?

True but this is making more space and weight available.

The reason why I'am thinking along these lines is we are going to come to a point when we cannot physicly get the missions we want into orbit in one piece. I'am thinking about some of the more elaberate (sp) rovers.

Imaging having a mars rover with a full chemistry lab, drilling rig, Nuke fuel cell and a large transmitter so we can get bigger pictures and maybe video in it moving on bigfoot sized wheels with a arial recon blimp etc...

[edit] you could also use it to build an "green house" to test what species of plant life could grown on the soil.

Once weight stops being a major concern you can start thinking wild!

joema
2005-Jan-17, 09:40 PM
Amadeus those are good questions. Back when more ambitious manned missions were planned, it was long assumed orbital assembly would be necessary. This was seriously considered for Apollo before deciding on the now familiar design.

Orbital assembly was likewise presumed for the manned Mars program envisioned to follow Apollo. So it's not a new idea.

However for manned missions you've got people up there anyway, whether they assemble vehicles or not. It's not an extra cost.

For unmanned probes, it would generally require (at least) triple launches: two unmanned launches carrying part A and B of the probe, and a manned launch to ferry up astronauts to assemble it. The cost of that would be high.

Also, as seen with the current HST servicing dilemma, astronaut availability isn't always guaranteed.

Other reasons are

(1) No need for that much payload in a single probe. With technical advances (miniaturization, efficiency) it's less necessary to have gigantic probes.

(2) Lack of funds for a single mega-size probe. Probe costs tends to scale with weight. It was almost impossible to get funds for Voyager, Galileo and Cassini AS IS. Imagine needing FIVE TIMES the money because the probe is twice as heavy, plus requires a separate manned launch to assemble it. Yet the scientific return would not be twice as much.

(3) No wish to put "all eggs in one basket". If a single mega probe fails, you've lost everything. That was a big risk on Cassini, fortunately it's working OK. Current thinking is using two or more smaller probes.

(4) In general current launchers have the needed capacity for currently affordable probes. It's true the Titan IV is being phased out, but Delta IV Heavy is coming on line, and upgrades to that can launch any currently planned probe. Delta IV is a modular design -- you strap together more boosters for more payload. Possible upgrades and derivatives could theoretically launch payload equal to a Saturn V. See http://www.boeing.com/defense-space/space/bls/d4heavy/docs/delta_growth_options.pdf

Collectively all these have so far eliminated the need for orbital assembly of unmanned space probes.

Kizarvexis
2005-Jan-17, 11:33 PM
(4) In general current launchers have the needed capacity for currently affordable probes. It's true the Titan IV is being phased out, but Delta IV Heavy is coming on line, and upgrades to that can launch any currently planned probe. Delta IV is a modular design -- you strap together more boosters for more payload. Possible upgrades and derivatives could theoretically launch payload equal to a Saturn V. See http://www.boeing.com/defense-space/space/bls/d4heavy/docs/delta_growth_options.pdf

The D-IV modular design is really cool. Besides having a target of 100 tons for the next-gen D-IV, does anyone know if there are any plans for a manned D-IV design?

Kizarvexis