Author Topic: SEP propulsion from LEO to LLO, Mars orbit, asteroid belt  (Read 10100 times)

Offline neviden

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What is the cheapest/fastest/most efficient way to convert sunlight to propulsion?

Offline nacnud

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Re: SEP propulsion from LEO to LLO, Mars orbit, asteroid belt
« Reply #1 on: 12/15/2006 09:27 am »
Light sail?

Offline meiza

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Re: SEP propulsion from LEO to LLO, Mars orbit, asteroid belt
« Reply #2 on: 12/15/2006 11:07 am »
Whaddya mean fast? Big delta vee or high acceleration?

Offline Joffan

You seem to have the expected answer in your title, Solar Electric Propulsion (ion drive), and I think at present that is the only direct use of sunlight that's been shown viable. The trade off is that the acceleration is low but the achievable delta-v (at least inside Mars orbit) is high , particularly in relation to the mass of propellant carried.

Solar sails are simple in principle but use only the momentum of the light, not its EM energy, so they have even lower accelerations. With no propellant the delta-v appears effectively unlimited, if you have enough time. Experience with ISS shows that even in space, things wear out,  so the delta-v will in reality be limited but the engineering detail will determine what the limit might be.
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Offline neviden

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Re: SEP propulsion from LEO to LLO, Mars orbit, asteroid belt
« Reply #4 on: 12/15/2006 12:02 pm »
fast as in.. few months to a year to get from LEO to any of those places.. light sail is nice, because you don't need propelant, but how big would it have to be to send 100 t from LEO to any of those places?

edit: ups.. you are right.. no, i did not expect any specific form of propulsion.. only that if we realy need nuclear reactor (it's expensive) if we got one working nearby (sun)..

Offline SteveMick

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Re: SEP propulsion from LEO to LLO, Mars orbit, asteroid belt
« Reply #5 on: 12/18/2006 06:05 pm »
Please see my post in the NEP to mars thread re: solar thermal/electric propulsion or ST/EP.
By using concentrated sunlight to directly heat hydrogen or another propellent accelerations up to about 1/10th gee are possible. By using a series of thrusts at perigee, such a system can raise its orbit and acheive escape to a Mars trajectory in about a week. Solar electric propulsion can then be used to shorten transit time. This is the fastest cheapest and most developed alternative to much slower chemical propulsion.
 Despite the Starfire program run out of Glenn Spaceflight center building and successfully testing a solar thermal rocket in 2002 which was intended for launch in 2004 I believe, this tech remains virtually unknown. I have written and presented papers over 20 years on this subject and still find myself regularly explaining to very knowledgeable people this basic technology.
Steve

Offline meiza

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Re: SEP propulsion from LEO to LLO, Mars orbit, asteroid belt
« Reply #6 on: 12/18/2006 06:17 pm »
What's a realistic ISP for those 1/10th gee kicks?

Offline SteveMick

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Re: SEP propulsion from LEO to LLO, Mars orbit, asteroid belt
« Reply #7 on: 12/22/2006 05:48 pm »
Great question and one whose answer depends on many assumptions and/or guesses particularly when someone of  my rather limited ability is trying to figure it out, but here goes.
The most critical parameter is concentrator mass per quantity of solar energy focussed. As I've mentioned there are various theoretical types of advanced concentrators; the best of which is a diamond film simple lens light net. Such concentrators could have a specific power of maybe a MW/lb at 1 AU. However a reasonable concentrator mirror using today's tech would be around 5KW/lb. or maybe a little better. If the overall efficiency to actual power in the thrust is 50% (maybe this is a little optimistic) then 2.5KW is available to heat propellent for each lb. of  concentrator mass. If the concentrator was 1/3 of the total mass at LEO, then .8KW is available per lb. of total mass for heated propellent. The amount for 1/10g acceleration would be 8KW/lb.of thrust. I estimate this to be in the 400 to 500 sec. range with hydrogen but I'm a little pushed for time(when you barely know how to figure something out it takes longer and we're leaving work now for the holiday) to figure out what the Isp actually is - I'll have to get back to you on that.
I realise that the concentrator being 1/3 the mass is a lot but it can be the power and propulsion for a payload so maybe it is reasonable. Also lower accelerations are fine for all but the last thrust. You're still talking about only a week or so from LEO to escape.
Steve

Offline yinzer

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Re: SEP propulsion from LEO to LLO, Mars orbit, asteroid belt
« Reply #8 on: 12/22/2006 07:23 pm »
The exhaust power is equal to F * Ve / 2, where F = force and Ve = exhaust velocity (Isp/g).  It's also m * a * Ve / 2, where m is the mass of the stage and a is the acceleration.  Using the latter formula, if you want to acceleration to be 1 m/s^2, and you have 1 kW of power per kilogram of mass, you can rewrite this to 1kW = 1m/s * Ve.  So Ve = 1000 m/s, or an Isp of 100 seconds.  To get 0.1g acceleration at an Isp of 400 seconds, you'd need 4 kW of exhaust power per kg of spacecraft.

Rocket engines are much more powerful than people give them credit for.
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Offline A_M_Swallow

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Re: SEP propulsion from LEO to LLO, Mars orbit, asteroid belt
« Reply #9 on: 05/05/2008 03:50 am »
Estimating the cost of a small SEP Ferry.

A full estimate would consider all the steps to make a SEP Ferry but the cost can be estimated by looking at the known costs of an existing SEP vehicle - the DAWN probe.  DAWN has an estimated budget of about $500 million of which $327 million was spent during development.
Reference NASA press release 06-108
http://www.nasa.gov/home/hqnews/2006/mar/HQ_06108_Dawn_reinstates.html

A SEP Ferry will need more thrust than DAWN so more/bigger ion thrusters, solar panels and fuel tank are required.  The ferry will also need a cargo area, rendezvous system and possibly an arm.  It will not need the scientific equipment such as the spectrometers.  This suggests a price of about $350 million plus launch cost.

p.s.  The larger SEP Ferries will also have very high solar panel costs.

Offline khallow

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Re: SEP propulsion from LEO to LLO, Mars orbit, asteroid belt
« Reply #10 on: 05/07/2008 03:15 pm »
Another thing to recall here is that the more patient you are, the lower delta v you need due to gravity assist trajectories.

joffan, the momentum of a photon is proportional to its energy (which is the same as its "EM" energy). It is exactly the energy of the photon divided by the speed of light.
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Offline wingod

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Re: SEP propulsion from LEO to LLO, Mars orbit, asteroid belt
« Reply #11 on: 05/07/2008 05:12 pm »
Quote
A_M_Swallow - 4/5/2008  10:50 PM

Estimating the cost of a small SEP Ferry.

A full estimate would consider all the steps to make a SEP Ferry but the cost can be estimated by looking at the known costs of an existing SEP vehicle - the DAWN probe.  DAWN has an estimated budget of about $500 million of which $327 million was spent during development.
Reference NASA press release 06-108
http://www.nasa.gov/home/hqnews/2006/mar/HQ_06108_Dawn_reinstates.html

A SEP Ferry will need more thrust than DAWN so more/bigger ion thrusters, solar panels and fuel tank are required.  The ferry will also need a cargo area, rendezvous system and possibly an arm.  It will not need the scientific equipment such as the spectrometers.  This suggests a price of about $350 million plus launch cost.

p.s.  The larger SEP Ferries will also have very high solar panel costs.

Funny, SMART-1 only cost 110 million Euros and went from the Earth into lunar orbit.



Offline A_M_Swallow

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Re: SEP propulsion from LEO to LLO, Mars orbit, asteroid belt
« Reply #12 on: 05/07/2008 05:59 pm »
Quote
wingod - 7/5/2008  6:12 PM

Funny, SMART-1 only cost 110 million Euros and went from the Earth into lunar orbit.

110 million euros is about 170 million U.S. dollars, approximately half the cost of DAWN.

SMART-1 was made in Sweden.  NASA and its main contractors do not have a large research establishment in Sweden so will probably have to pay U.S. wages.

To permit a space-line to make a profit from a tramp SEP Ferry tight cost control is likely to be needed during design and manufacturing.

Offline wingod

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Re: SEP propulsion from LEO to LLO, Mars orbit, asteroid belt
« Reply #13 on: 05/07/2008 06:21 pm »
Quote
A_M_Swallow - 7/5/2008  12:59 PM

Quote
wingod - 7/5/2008  6:12 PM

Funny, SMART-1 only cost 110 million Euros and went from the Earth into lunar orbit.

110 million euros is about 170 million U.S. dollars, approximately half the cost of DAWN.

SMART-1 was made in Sweden.  NASA and its main contractors do not have a large research establishment in Sweden so will probably have to pay U.S. wages.

To permit a space-line to make a profit from a tramp SEP Ferry tight cost control is likely to be needed during design and manufacturing.

Do you really mean to insult Swedes in this fashion?  At the time that SMART-1 was built the Euro was trading at 80 cents to the dollar. so that is really about $100 million dollars.

I am really amazed at the level of ignorance here about Europe.  They have been a fully integrated part of the global aerospace enterprise and Priordia net is a major global ground station enterprise.  Since I work quite a lot with Swedes I can inform you that they pay them just as much as Americans make.



Offline GuessWho

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RE: SEP propulsion from LEO to LLO, Mars orbit, asteroid belt
« Reply #14 on: 05/07/2008 08:14 pm »
A solar thermal rocket can generally achieve Isp's in the range of 800-840 seconds corresponding to an exit gas temperature of 2350K - 2550K.  Thrust levels are dictated by primary concentrator size in the case of "direct gain" engines and by a combination of primary concentrator sixe and thermal energy storage mass in the case of "impulsive burn" engines.

Offline wingod

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Re: SEP propulsion from LEO to LLO, Mars orbit, asteroid belt
« Reply #15 on: 05/07/2008 10:56 pm »
Quote
A_M_Swallow - 7/5/2008  1:57 PM

Quote
wingod - 7/5/2008  7:21 PM
Do you really mean to insult Swedes in this fashion?  At the time that SMART-1 was built the Euro was trading at 80 cents to the dollar. so that is really about $100 million dollars.

You are in a bad mood today.

The Euro-dollar has changed since the Wiki page was entered.

How about the fact that I just helped to chair the preliminary design of a small SEP tug and know exactly what the costs are and know that your numbers are completely meaningless.  The prime contractor is Swedish Space.  It does insult me when you imply that Swedish engineers are any less capable or any less well compensated as American ones and that is the reason that SMART-1 was  less costly than Dawn.

I have worked in Europe off an on for the past seven years and know exactly what the exchange rates were and are.



Offline A_M_Swallow

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Re: SEP propulsion from LEO to LLO, Mars orbit, asteroid belt
« Reply #16 on: 05/08/2008 04:44 pm »
Quote
SteveMick - 18/12/2006  7:05 PM

By using concentrated sunlight to directly heat hydrogen or another propellent accelerations up to about 1/10th gee are possible. By using a series of thrusts at perigee, such a system can raise its orbit and acheive escape to a Mars trajectory in about a week. Solar electric propulsion can then be used to shorten transit time. This is the fastest cheapest and most developed alternative to much slower chemical propulsion.

Steve Mick any chance of making it 2/10th gee?

Lunar gravity is 0.1654g (1.622 m/s/s).  At 0.2g a solar thermal rocket would be used in lunar landers and ascent stages.  An ISP of 800 would a large increase in the mass of lunar payloads.  The Apollo LEM had an ISP of 311.
« Last Edit: 09/20/2008 04:35 am by A_M_Swallow »

Offline A_M_Swallow

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Re: SEP propulsion from LEO to LLO, Mars orbit, asteroid belt
« Reply #17 on: 05/12/2008 03:32 am »
Quote
wingod - 7/5/2008  11:56 PM

How about the fact that I just helped to chair the preliminary design of a small SEP tug and know exactly what the costs are and know that your numbers are completely meaningless.

The other way of performing an external estimate is to realise that the SEP tug is doing the same job as the Earth Departure Stage.  This will be using the J-2X rocket motor.  NASA is paying $1.2 billion to Pratt and Whitney Rocketdyne Inc. just to test and develop the engine.  This would imply a SEP tug development cost of over $1 billion if performed by NASA.
http://www.nasa.gov/home/hqnews/2007/jul/HQ_C07030_J2X_Contract_prt.htm
You appear to be claiming that the Swedes can do this for about 1/10 the price.

Offline A_M_Swallow

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Re: SEP propulsion from LEO to LLO, Mars orbit, asteroid belt
« Reply #18 on: 03/25/2009 04:30 am »
If NASA decided it wanted to build a solar powered space tug could it have cost estimated available by September?  The tug could be solar electric or solar thermal.

Edit c/./?/
« Last Edit: 03/25/2009 04:31 am by A_M_Swallow »

Offline space_man

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Re: SEP propulsion from LEO to LLO, Mars orbit, asteroid belt
« Reply #19 on: 04/09/2009 03:37 pm »
Here is another way to utilize solar power for propulsion.

This is in essence a combined electrical/chemical engine.

I propose to attach a small electrical motor to the LOX pump and another one to the LH2 pump (The motors will be different in size due to varying flow requirements). One immidiate advantage is that you dont need a transmission, gas generator, turbine,etc...(less weight). A sollar array mounted to the engine powers the electric motors which slowly push propellants into the combustion chamber.

I understand the thrust will be quite small due to the low flow-rate but it will be consistent and last a while. The biggest savings is that you do not waste propellants on driving the turbopumps which should increase the specific impulse of the engine. The best application for this would be transfer-orbit injections.

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