Author Topic: Manned Circumnavigation of the Inner Solar System  (Read 101883 times)

Offline rklaehn

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Re: Manned Circumnavigation of the Inner Solar System
« Reply #20 on: 02/14/2009 08:53 am »
What would the bandwidth requirements be for streaming IMAX quality video? During the fly-bys, of course, especially if small cameras could be deployed in constellations, each camera linked to the mother ship.

I am not sure about the exact bandwidth requirements, but doing a live stream with normal radio frequency technology would definitely require cooperation from the NASA deep space network. I am not sure whether NASA would support such a mission with little scientific value for free.

An alternative would be laser communication to a satellite in GEO. That would certainly provide more than enough bandwidth. And the technology is available now: http://www.tesat.de/product_lines/optical_products/optical_products.html, so it should be commercial off the shelf when this hypothetical mission launches.

Offline rklaehn

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Re: Manned Circumnavigation of the Inner Solar System
« Reply #21 on: 02/14/2009 09:06 am »
Quote
Instead of a typical bigelow module the company could be contracted out to make a roughly wheel shaped hab .
I think the Rigid Station 2 intended to be launched by a Saturn V would be a good starting point.
http://www.astronautix.com/craft/selation.htm
This can be made to fit inside one J120 with an upper stage.
Also it has six sections which means redundancy .

I think this is way too big for an initial interplanetary mission. A single small bigelow habitat is completely sufficient for one person. For artificial gravity, use the upper stage as a counterweight with a rotating tether like proposed in mars direct.

But even zero gravity would be acceptable. The explorer would have all day to exercise, and somebody who is crazy enough to embark on such a dangerous mission is probably not that concerned about bone loss anyway.

Quote
As for propulsion use  two VASIMR engines for departure.
http://www.adastrarocket.com/home1.html

A VASIMR engine would require a nuclear reactor or a giant solar array to power it. And even then it would not have enough thrust to do a trans mars or trans venus injection burn deep in the earth gravity well.

You could use a low-thrust engine such as VASIMR to get the ship from LEO to a highly elliptical orbit, but the departure burn needs to be done with a high thrust engine.

Offline Ben the Space Brit

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Re: Manned Circumnavigation of the Inner Solar System
« Reply #22 on: 02/14/2009 10:05 am »
A VASIMR engine would require a nuclear reactor or a giant solar array to power it. And even then it would not have enough thrust to do a trans mars or trans venus injection burn deep in the earth gravity well.

You could use a low-thrust engine such as VASIMR to get the ship from LEO to a highly elliptical orbit, but the departure burn needs to be done with a high thrust engine.

So, how about using the Castor SRM suggested by rklaehn as the EDS and keep an SEP VASMIR as the sustainer/course correction motor? 

Cover the exterior of the Sundancer hab module with product logos and put webcams on the solar arrays outboard ends to take regular photos of the adverts in space.  Inside, do lots of long-term freefall aeroponics & biomedical experiments.  For safety's sake, I'd recommend a minimum crew of two, say a rich madman (*cough*SirRichardBranson*cough*) and a sufficiently rich pilot/adventurer.  Ensure that there is plenty of product placement on the supplies (food with retail-style manufacturers' labels, laptops with the manufacturer's logo painted on the back of the flip-up cover etc.).

Finally - Video blog, video blog, video blog.  Even if nothing much is actually happening, millions will want to know about it.  The actual flybys would need to be streamed live with pictures of the 'drop off' probes being released being particularly important high points, IMHO.
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Offline rklaehn

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Re: Manned Circumnavigation of the Inner Solar System
« Reply #23 on: 02/14/2009 10:29 am »
So, how about using the Castor SRM suggested by rklaehn as the EDS and keep an SEP VASMIR as the sustainer/course correction motor? 

A high-ISP/low thrust engine would certainly be useful for mid course corrections. But VASIMIR is too big for such an application. And besides, it is not even clear if it will work as advertized.

A hall effect thruster such as one of these http://www.busek.com/halleffect.html would make much more sense.

But you might be able to do this just with chemical propellant. The sundancer module has its own propulsion system, so you might just want to use that for mid-course corrections in order to keep the whole mission as simple as possible.

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Finally - Video blog, video blog, video blog.  Even if nothing much is actually happening, millions will want to know about it.  The actual flybys would need to be streamed live with pictures of the 'drop off' probes being released being particularly important high points, IMHO.

I agree. That is why a high-bandwidth laser link to earth would be very helpful.

One thing that would be nice would be a few small companion satellites with HDTV cameras that could film the spacecraft from a distance. Wasn't something like this planned for ISS?

Offline EE Scott

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Re: Manned Circumnavigation of the Inner Solar System
« Reply #24 on: 02/14/2009 12:25 pm »
Tens of billions of dollars? Why so much? A billion dollars, maybe two or three billion but not ten.

Yes, it could definitely be done on the cheap - but that's not how I would do it.  If I had the money, I would spend some extra $$ for as comfortable and robust a spacecraft as I could muster within a reasonable timeframe.

The proposals for streaming HD video and whatnot are very exciting.   There could be some mindblowing stuff to come out of a mission like this.  When I think of all the pork that will be attached to the so-called stimulus bill, and just to strip a few billion off of it (which would not even be missed) to get a mission like this done, it gets frustrating.  All the years of "there's no money" to get something ambitious done, yet at the first sign of a recession they print a trillion dollars to stimulate the economy - why not stimulate the aerospace sector with some funds, energy and adventure?  OK, I'll stop going OT.

Love reading about these types of missions!
« Last Edit: 02/14/2009 12:26 pm by EE Scott »
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Offline kfsorensen

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Re: Manned Circumnavigation of the Inner Solar System
« Reply #25 on: 02/14/2009 12:32 pm »
A high-ISP/low thrust engine would certainly be useful for mid course corrections. But VASIMIR is too big for such an application. And besides, it is not even clear if it will work as advertized.

A hall effect thruster such as one of these http://www.busek.com/halleffect.html would make much more sense.

Agreed.  This is a mission where you're trying to keep costs and tech developments to a minimum.  Most of the effort will be in a life support system that can keep this guy alive for two years in a variety of solar insolation levels and radiation fluxes.

The whole point of the trajectory is that, once launched, no "deterministic delta-V" maneuvers are required.  It's all course corrections til you get back to Earth.  Venus and Mars's gravity does all the work for you, which is pretty remarkable to take a cruise like this and never have to "hit the gas".

Offline rklaehn

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Re: Manned Circumnavigation of the Inner Solar System
« Reply #26 on: 02/14/2009 12:54 pm »
Tens of billions of dollars? Why so much? A billion dollars, maybe two or three billion but not ten.

Yes, it could definitely be done on the cheap - but that's not how I would do it.  If I had the money, I would spend some extra $$ for as comfortable and robust a spacecraft as I could muster within a reasonable timeframe.

It is very fun to speculate what one could do with tens of billions. But I think it is much more useful to design a low-cost mission. This does not have to be a pleasure cruise. In fact a guy squeezing into a tiny capsule filled with supplies would be much more heroic.

And a sundancer would be extremely comfortable anyway. It has more cubic meters than my apartment :-)

A high-ISP/low thrust engine would certainly be useful for mid course corrections. But VASIMIR is too big for such an application. And besides, it is not even clear if it will work as advertized.

A hall effect thruster such as one of these http://www.busek.com/halleffect.html would make much more sense.

Agreed.  This is a mission where you're trying to keep costs and tech developments to a minimum.  Most of the effort will be in a life support system that can keep this guy alive for two years in a variety of solar insolation levels and radiation fluxes.

Sundancer is supposed to have a life support system capable of supporting three crew for six months, so one person for two years should be doable. More than one person would be a stretch.

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The whole point of the trajectory is that, once launched, no "deterministic delta-V" maneuvers are required.  It's all course corrections til you get back to Earth.  Venus and Mars's gravity does all the work for you, which is pretty remarkable to take a cruise like this and never have to "hit the gas".

I think the bigelow module propulsion system should be more than enough for these course corrections. But the spacex payload numbers for GTO seem extremely optimistic to me. Maybe the "GTO mass to orbit" of 15,010 kg is the total mass including the upper stage.

What is the delta-v for a grand tour anyway? In the paper they mention 13 900 fps, which is 4 236.72 m / s. Is that from LEO?

Offline kfsorensen

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Re: Manned Circumnavigation of the Inner Solar System
« Reply #27 on: 02/14/2009 01:31 pm »
What is the delta-v for a grand tour anyway? In the paper they mention 13 900 fps, which is 4 236.72 m / s. Is that from LEO?

The DV to start the tour varies from opportunity to opportunity.  The 1977 numbers were specific to that particular mission.  At any rate, the initial DV to start the tour would be provided by the upper stage of the launch vehicle.  We would base our mass calculations on the launch capabilities of the vehicle to the particular orbital energy (C3) required to start the tour.

Once injected, the DV requirements for course corrections should be relatively modest and on the order of what the Bigelow Sundancer is already required to have for orbital maintenance in LEO.  Possibly lower.

Offline rklaehn

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Re: Manned Circumnavigation of the Inner Solar System
« Reply #28 on: 02/14/2009 01:48 pm »
The DV to start the tour varies from opportunity to opportunity.

Of course. But a rough ballpark number for delta-v from LEO or C3 would be useful for back of the envelope calculations.

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The 1977 numbers were specific to that particular mission.  At any rate, the initial DV to start the tour would be provided by the upper stage of the launch vehicle.

Unfortunately there is no launch vehicle that can send a 15t stack (sundancer and dragon) to escape velocity. A propellant depot would help.
« Last Edit: 02/14/2009 02:28 pm by rklaehn »

Offline kfsorensen

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Re: Manned Circumnavigation of the Inner Solar System
« Reply #29 on: 02/14/2009 03:22 pm »
Unfortunately there is no launch vehicle that can send a 15t stack (sundancer and dragon) to escape velocity. A propellant depot would help.

Too expensive and complicated.  The capability of the launch vehicle to the throw conditions would have to be the limiting factor on the mass that could go along for the mission.  In-orbit rendezvous and propellant transfer would totally bust the budget for this type of activity.

Offline Patchouli

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Re: Manned Circumnavigation of the Inner Solar System
« Reply #30 on: 02/14/2009 03:40 pm »
Quote
Instead of a typical bigelow module the company could be contracted out to make a roughly wheel shaped hab .
I think the Rigid Station 2 intended to be launched by a Saturn V would be a good starting point.
http://www.astronautix.com/craft/selation.htm
This can be made to fit inside one J120 with an upper stage.
Also it has six sections which means redundancy .

I think this is way too big for an initial interplanetary mission. A single small bigelow habitat is completely sufficient for one person. For artificial gravity, use the upper stage as a counterweight with a rotating tether like proposed in mars direct.

But even zero gravity would be acceptable. The explorer would have all day to exercise, and somebody who is crazy enough to embark on such a dangerous mission is probably not that concerned about bone loss anyway.

Quote
As for propulsion use  two VASIMR engines for departure.
http://www.adastrarocket.com/home1.html

A VASIMR engine would require a nuclear reactor or a giant solar array to power it. And even then it would not have enough thrust to do a trans mars or trans venus injection burn deep in the earth gravity well.

You could use a low-thrust engine such as VASIMR to get the ship from LEO to a highly elliptical orbit, but the departure burn needs to be done with a high thrust engine.

I was not thinking a single person but more along the lines of the arctic expeditions of the past where the explorer brings along a half dozen or more crew.
You'll need a crew as keeping the ship running will be far to much work load for a single person to handle.

As for using VASIMR for the injection burn you can but it'll take 30 days to spiral out of earth's gravity well.
It's performance is far above a hall thruster which I believe will be largely obsolete for this task in 10 to 20 years.
This why I'd have the ship spiral out to L1 or at least 80,000km and the crew rides some small fast vehicle to rendezvous with it.

Using chemical for the injection burn you get stuck with using a monster stage like the EDS or a wide body centaur and this equals big $$$$.

We're talking at least 15,000kg that needs to be place on an escape trajectory.

I'll be more realistic and go with 20,000 to 35,000Kg as these things always end up heavier then expected.

Though a refueled F-9 upper stage with stretched tanks could be used as a low cost injection stage and storing LOX and kerosene is going to be easier then hydrogen.

A block DM may not have enough impulse to even get the ship into GTO let alone escape.
This is assuming the lightest combo a Sundancer and a Soyuz and three crew which should come in around 15,800kg though add an extra 3,000 to 5000kg of consumables to that plus extra solar collectors to power the energy hungry air and water recycling equipment.
Just carrying all the food you need will be lighter then any closed loop system.
So the lightest possible mission would be around 20,000Kg it would fit on an EELV,F9 or in the back of a shuttle.
I guess a Centaur might be able pull off being the injection stage here.
The hard part would be getting it into LEO without burning much of it's propellant.
Though if you have a J-120 it all becomes easier though I wonder if an F9-H with a Centaur resized for the vehicle also could send the stack to escape velocity if the J-120 is not available or with in budget.
Orbital rendezvous and or refueling will be an absolute necessity unless an LV of 45T payload or more is used.
The easiest I think would be to split the payload into two 20T and 30T sections and dock them in LEO.
This would entitle making a Centaur reach orbit with nothing more then a docking adapter and wait for the rest of the payload to rendezvous with it.
One big fear I have about a small crew in a small vehicle on long missions is the possibility they will kill each other.
The data from simulated Mars missions done by the Russian space agency is anything but encouraging.



« Last Edit: 02/14/2009 04:18 pm by Patchouli »

Offline Bill White

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Re: Manned Circumnavigation of the Inner Solar System
« Reply #31 on: 02/14/2009 04:14 pm »
Why not use two or three or even four Block Ds, if necessary?

Buy them off the shelf and design the attachment points so they can fire simultaneously.

= = =

A single Jupiter 120 would seem sufficient to loft the habitat and an RL-10 based Earth Departure Stage. ~$250 / ~$300 million for the launch, right? If we trust Ross's figures & if US Congress agrees to sell a launch.

- or -

Use 3 or 4 Protons and maybe even incorporate a Fregat or two into the Sundancer and use a Fregat to decelerate the re-entry capsule before returning to Earth atmosphere.

$500 million for four Proton launches, as a package deal? Reasonable or not? Loft the habitat and the Block Ds and assemble on orbit.

Aren't there "Proton Mars" scenarios out there?

Or, use a smaller habitat and "rough it" more at a much lower cost.

= = =

Free flying camera modules could also be deployed AFTER the Venus insertion burn with solar sail experiments being conducted by using those camera modules to maneuver around the Sundancer.


EML architectures should be seen as ratchet opportunities

Offline kfsorensen

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Re: Manned Circumnavigation of the Inner Solar System
« Reply #32 on: 02/14/2009 04:15 pm »
No matter how rich the person who might mount this mission they're going to be way more cost-conscious than an agency like NASA.  The "arctic" expedition you're talking about is way too complicated.

Listen, all this person has to do is sit in a can and survive for two years.  That's no "workload".  The more people you bring along, the more radical propulsion systems you want, the more orbital operations you add, the more unappealing your mission architecture is.

People have gotten in rather small sailboats and sailed around the world solo.  This is more analogous to that, but with far less workload.  Every 90 days or so, the pilot will do a course correction.  The rest of the time he'll be reading and answering email.  Three times on the mission he'll have a wondrous sight out the porthole.  At the very end he'll go screaming through hell on the way in.

A Soyuz is way too big and heavy for this mission.  All the pilot needs to do is survive reentry, slow to subsonic velocities, and bail out and parachute to the ground.  He doesn't need a big fancy Soyuz reentry capsule for that.  He needs a good parachute and minimally sized aeroshell.
« Last Edit: 02/14/2009 04:18 pm by vanilla »

Offline Kaputnik

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Re: Manned Circumnavigation of the Inner Solar System
« Reply #33 on: 02/14/2009 05:56 pm »
A Soyuz is way too big and heavy for this mission.  All the pilot needs to do is survive reentry, slow to subsonic velocities, and bail out and parachute to the ground.  He doesn't need a big fancy Soyuz reentry capsule for that.  He needs a good parachute and minimally sized aeroshell.

More than big enough, yes, but is it worth building a bespoke capsule at higher cost, just to save a couple of tonnes of mass taken along?
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Offline rklaehn

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Re: Manned Circumnavigation of the Inner Solar System
« Reply #34 on: 02/15/2009 10:26 am »
As for using VASIMR for the injection burn you can but it'll take 30 days to spiral out of earth's gravity well.

To spiral out in 30 days you would need a solar array larger than the ISS solar array. I really don't see how something like this is doable even for somebody willing to spend a billion.

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It's performance is far above a hall thruster which I believe will be largely obsolete for this task in 10 to 20 years.

Depends on what your performance metric is. The specific impulse is higher. But just that means that you need a huge power source. VASIMIR has a specific impulse of 3000-30000, which is much too high for getting high thrust with a realistic power source.

(a VASIMIR thruster with an ISP of 3000s will use four times the energy for the same thrust as a hall effect thruster with an ISP of 1500s)

VASIMIR only really makes sense if you have a nuclear reactor. As long as there are no commercial off the shelf space nuclear reactors, just forget about VASIMIR.

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This why I'd have the ship spiral out to L1 or at least 80,000km and the crew rides some small fast vehicle to rendezvous with it.

Using chemical for the injection burn you get stuck with using a monster stage like the EDS or a wide body centaur and this equals big $$$$.

You can spiral out to a highly elliptic earth orbit with electric propulsion. But you can not do the trans mars/trans venus injection maneuver with electric propulsion. You need a high thrust propulsion system that is capable of delivering the entire delta-v close to the perigee of the highly elliptic orbit in order for the oberth effect http://en.wikipedia.org/wiki/Oberth_effect to work.

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We're talking at least 15,000kg that needs to be place on an escape trajectory.

I'll be more realistic and go with 20,000 to 35,000Kg as these things always end up heavier then expected.

Using one or more existing storable propellant upper stages such as the CASTOR or Briz sequentially is still much more realistic than using an untested electric propulsion system that requires solar arrays the size of a football field.

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Though a refueled F-9 upper stage with stretched tanks could be used as a low cost injection stage and storing LOX and kerosene is going to be easier then hydrogen.

There is not enough information available for the falcon 9 upper stage, but with reasonable estimates (fueled mass about 50 tons, ISP 340s) even a full falcon 9 upper stage is not capable of sending a 15t spacecraft to trans-venus-injection.

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A block DM may not have enough impulse to even get the ship into GTO let alone escape.

That is correct. You would need at least two in a train configuration. Since the block DM has an orbital lifetime of 12 days, and even the russians can not do two proton launches in 12 days, it would probably be better to use "briz" storable propellant upper stages.

Quote
This is assuming the lightest combo a Sundancer and a Soyuz and three crew which should come in around 15,800kg though add an extra 3,000 to 5000kg of consumables to that plus extra solar collectors to power the energy hungry air and water recycling equipment.
Just carrying all the food you need will be lighter then any closed loop system.
So the lightest possible mission would be around 20,000Kg it would fit on an EELV,F9 or in the back of a shuttle.

If you want three crew that is correct. For one crew you would be able to use more or less the standard sundancer life support system and you need less consumables, so I think 15000kg is doable.

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I guess a Centaur might be able pull off being the injection stage here.
The hard part would be getting it into LEO without burning much of it's propellant.

Unfortunately not. I did some calculations with the delta heavy upper stage, and it has just barely enough delta-v to send the ship to an escape trajectory.

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One big fear I have about a small crew in a small vehicle on long missions is the possibility they will kill each other.
The data from simulated Mars missions done by the Russian space agency is anything but encouraging.

One more argument to send just one person :-)

People are in much more extreme situations all the time. Compared to what soldiers have to endure during a war, this is almost a luxury cruise.

Offline rklaehn

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Re: Manned Circumnavigation of the Inner Solar System
« Reply #35 on: 02/15/2009 11:04 am »
Why not use two or three or even four Block Ds, if necessary?

The Block DM is a cryogenic upper stage and has an orbital life time of just 12 days. So when using more than one you might be better off with a storable propellant upper stage such as the briz. But then you might as well go all american to avoid ITAR and political issues and use the CASTOR-30 upper stage.

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Buy them off the shelf and design the attachment points so they can fire simultaneously.

You do not want them to fire simultaneously. I think the best way would be to stack them and use them sequentially. The first two get the spacecraft from LEO into a highly elliptic orbit, and the third does the trans-venus injection burn.

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A single Jupiter 120 would seem sufficient to loft the habitat and an RL-10 based Earth Departure Stage. ~$250 / ~$300 million for the launch, right? If we trust Ross's figures & if US Congress agrees to sell a launch.

That is a pretty big assumption. Given all the trouble dennis tito had just visiting the ISS, I don't think that NASA would be willing to sell a jupiter. A privately financed interplanetary mission would be a huge embarrasment for nasa, so I think they would try to fight it.

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Or, use a smaller habitat and "rough it" more at a much lower cost.

That would be an alternative: just use a dragon capsule full of supplies for a one-person mission. A dragon capsule has a dry weight of about 4200kg and a maximum pressurized volume of 10m3 according to this brochure. So this would be very claustrophobic, but definitely doable.

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Free flying camera modules could also be deployed AFTER the Venus insertion burn with solar sail experiments being conducted by using those camera modules to maneuver around the Sundancer.

Yes, that was the idea. They would probably dock to the main spacecraft for all course correction maneuvers.

Another good idea might be to give away secondary payload slots (50-100kg) for planetary landers to universities. These would be sitting in the dragon trunk for the transit and would be released during the flybys.

Here is one project that would make a great secondary payload: archimedes.
« Last Edit: 02/15/2009 11:33 am by rklaehn »

Offline rklaehn

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Re: Manned Circumnavigation of the Inner Solar System
« Reply #36 on: 02/15/2009 11:23 am »
People have gotten in rather small sailboats and sailed around the world solo.  This is more analogous to that, but with far less workload.  Every 90 days or so, the pilot will do a course correction.  The rest of the time he'll be reading and answering email.  Three times on the mission he'll have a wondrous sight out the porthole.  At the very end he'll go screaming through hell on the way in.

I also think that human factors won't be a problem. In many ways a single person mission would be less problematic than a two person mission in close quarters.

A Soyuz is way too big and heavy for this mission.  All the pilot needs to do is survive reentry, slow to subsonic velocities, and bail out and parachute to the ground.  He doesn't need a big fancy Soyuz reentry capsule for that.  He needs a good parachute and minimally sized aeroshell.

It would be great if a one person reentry capsule existed. But in order for this to be even remotely realistic, we have to work with what exists or will probably be available.

Dragon has an empty weight of 4200kg and an internal volume of 10m3, so if you want a really minimalistic mission, just use a modified dragon with all but one seat removed and fitted with a toilet and a life support system.

Offline Ben the Space Brit

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Re: Manned Circumnavigation of the Inner Solar System
« Reply #37 on: 02/15/2009 01:13 pm »
A single Jupiter 120 would seem sufficient to loft the habitat and an RL-10 based Earth Departure Stage. ~$250 / ~$300 million for the launch, right? If we trust Ross's figures & if US Congress agrees to sell a launch.

That is a pretty big assumption. Given all the trouble dennis tito had just visiting the ISS, I don't think that NASA would be willing to sell a jupiter. A privately financed interplanetary mission would be a huge embarrasment for nasa, so I think they would try to fight it.

Agreed.  Significant power blocs in NASA went through a whole period of hating commercial space (something that Mr. Tito's experiences were symptomatic).  Right now, they are tolerated, mostly because the US indigenous manned program goes into stasis for five years without it.  However, I can't see them co-operating with a program that would humiliate them (or be perceived by their political masters as a humiliation).  Yes, it is irrational but it is political, so, in some ways, it is meant to be irratonal.

That means that, if this is to go ahead, it has to be restricted to stuff that money can buy and would not be greatly impeded by political issues. 

Oddly enough, that does not rule out Lockheed-Martin or Boeing-MDD.  After the way NASA has maligned them over EELV as an Orion launch vehicle, something tells me that they would love to embarrass the agency, especially if it means DreamChaser/Atlas-V is operational (and effectively a CEV) before Orion even gets off the ground.
« Last Edit: 02/15/2009 01:15 pm by Ben the Space Brit »
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The Space Shuttle Program - 1981-2011

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Offline rklaehn

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Re: Manned Circumnavigation of the Inner Solar System
« Reply #38 on: 02/15/2009 01:45 pm »
I created a google spreadsheet with a quick BOTE mass analysis
http://spreadsheets.google.com/ccc?key=pU3-zin-3Rk-KyAlkUVYOXw

After doing some more calculations, the proton briz upper stage seems almost perfect for this job. It is very short and compact, so it should be easy to stack a few of them. And it uses storable propellants, so you could take your time assembling the stack in orbit.

It turns out that you need at least three to send a plausible ship to a tour trajectory.

While it is theoretically possible to use just a dragon without a sundancer, I think it does not make much sense. Most of the mass of the sundancer is stuff you will need anyway (life support system, additional solar cells, toilet), so just trying to squeeze all that into a dragon does not buy you much mass.

And since even a single, totally cramped dragon would require two briz stages, you need to develop the stacking technology in any case. So spending 100 million more to spend the two years in a module the size of an apartment instead of the size of a guest bathroom seems like a good investment.

Another great secondary payload would be a small telescope. There is a whole class of asteroids inside the earth orbit that are almost impossible to see from earth since they are not visible at night. Looking back out from venus, these would be relatively easy to spot.

Offline Kaputnik

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Re: Manned Circumnavigation of the Inner Solar System
« Reply #39 on: 02/15/2009 04:08 pm »
You can spiral out to a highly elliptic earth orbit with electric propulsion. But you can not do the trans mars/trans venus injection maneuver with electric propulsion. You need a high thrust propulsion system that is capable of delivering the entire delta-v close to the perigee of the highly elliptic orbit in order for the oberth effect http://en.wikipedia.org/wiki/Oberth_effect to work.

JPL did a study involving NEP whereby a spiralling TMI manoeuvre was used. I was a bit sceptical but apparently it would work. You'd need about 300ms for the final escape burn IIRC. I think that Vanilla knows the study quite well so may be able to correct me.
"I don't care what anything was DESIGNED to do, I care about what it CAN do"- Gene Kranz

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