Author Topic: Ion/vasimr tugs for non time critical cargo.  (Read 8941 times)

Offline Patchouli

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Ion/vasimr tugs for non time critical cargo.
« on: 03/28/2008 03:42 PM »
If they switch Altair to storable propellants and a private group builds a lander that uses them I think it also could make use of a solar electric tug to replace the EDS for some missions.

Use of the solar or nuclear electric tug wouldn't be for manned mission but for cargo missions such as hab sections,vehicles, and bulk cargo.

I think it could allow one Ares V to send two or three cargo landers vs one or a delta IV/F9-H plus one delta II class vehicle to refuel the tug to land sizable cargo on the moon.

Other Altair improvements this one is official nasa cannon according to flight global is use of a drop stage.

 This improves payload and gets it closer to the ground so you can get by with smaller cranes and or ramps to get it off the lander.

Or just expend the lander since it doesn't have to come back to lunar orbit and have athlete as the landing gear.

http://www.flightglobal.com/blogs/hyperbola/2008/03/altair-lunar-lander-expanding.html

Offline A_M_Swallow

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RE: Ion/vasimr tugs for non time critical cargo.
« Reply #1 on: 03/28/2008 07:27 PM »
Quote
Patchouli - 28/3/2008  4:42 PM

If they switch Altair to storable propellants and a private group builds a lander that uses them I think it also could make use of a solar electric tug to replace the EDS for some missions.

Use of the solar or nuclear electric tug wouldn't be for manned mission but for cargo missions such as hab sections,vehicles, and bulk cargo.

That is a little over restrictive.  A SEP ferry can be used for half of a manned mission.  The SEP brings the lander and fuel for the lander.  Approximately a year later a smaller EDS brings the CEV containing the people and the food.  They rendezvous in low lunar orbit (LLO) or at EML2.

If using Hall Effect ion thrusters with an ISP of 2750 and a LEO to LLO delta-v of 4.10 km/s allow 16.5% of mass for SEP fuel.  

More fuel is needed if the ferry is reusable.  The ferry could have been lifted off the Earth on a different Launch Vehicle.  This report estimates the SEP and solar arrays would have a mass of about 9.2 mT.
http://uk.wrs.yahoo.com/_ylt=A1f4cfiEU.1HOV0B.XpLBQx.;_ylu=X3oDMTE2dW5zM2pmBHNlYwNzcgRwb3MDMTIEY29sbwNpcmQEdnRpZANVSzA1MDFfNTAx/SIG=1235boedb/EXP=1206822148/**http%3A//www.entechsolar.com/SPRAT-XX-SLA-SEP.pdf

Offline Patchouli

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RE: Ion/vasimr tugs for non time critical cargo.
« Reply #2 on: 03/28/2008 08:00 PM »
I figure travel time could be less then one year since both the ion engines and the solar cells have greatly improved since those used on smart 1.

We have solar cells with nearly 50% efficiency now vs 35% on smart 1 and the dual gridded ion thruster with  much higher isp or the VASIMR rocket as good of ISP in high thrust mode and I think 7x better in low thrust mode.

I think the best ion engines under going testing they'll be ready by the time we fly to the moon now have an ISP of over 5000 sec and vasimr can reach over 10,000 sec already with 50,000 possible .

http://www.adastrarocket.com/Technology.html


This engine claims to be 10x more efficient then smart 1's engine whch should give it an ISP of 27,000.

http://www.physorg.com/news9786.html

Even if it only proves to be twice as efficient in practice it will make a reusable tug very practical.

Who knows maybe this tug could be Adastrarocket's chance to prove their technology.

Vasimr seems to be the best engine for use here because of it's performance and the solar array wouldn't be that large maybe 1/4 ISS's later tugs could even make use of beamed energy for higher performance.

Though if Altair used storable propellants the ion tug could transport the manned lander too.
 
We'd only need three tugs in service so there is always a tug waiting in LEO at any given time assuming the ESAS fight rate.

I figured only cargo because NASA might not let go of lH2 so a private lander would have to use the tug instead maybe something scaled up from the google lunar prize.

Spacedev's hybrid lander should have no issues at all with taking 3 to 12 months to reach the moon for example.

Though the NEP vasimr tug could take as little as 30 days based on the nasa study of a vasimr mars mission.

Time would be dependent on what engines are flying and the power to weight of the solar collectors or reactor and how much mass you want to saddle the tug with etc etc.

I figure 30KW would be a good starting point for solar power with 150-300KW a desirable goal esp if an HLLV like a cryo upper stage falcon 9-h, direct or ares V are available the tug is reusable and could last up to 15 years.

Online docmordrid

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RE: Ion/vasimr tugs for non time critical cargo.
« Reply #3 on: 03/28/2008 10:28 PM »
IIRC AdAstra's quote for the soon to be tested VASIMR prototype is 200kw.

EDIT: ah yes, here it is;

http://www.adastrarocket.com/Release%20040308final.pdf

Quote
Major 2007 milestones achieved included
key results from a newly operational
VASIMRô 100kW test bed, the VX-100
and initiation of manufacturing and
subsystem integration for the first flight-like
engine prototype, the 200kW VX-200. In
addition, the company signed important
agreements with NASA and NAUTEL Ltd
of Canada.
>
An initial test firing of the full engine
prototype has been postponed until the 2nd
quarter of 2008 in order to give Scientific
Magnetics of Culham, UK. the needed time
to complete its certification of the
superconducting subsystem. This is a critical
component of the engine, which the British
company is building under contract with Ad
Astra.
DM

Offline alexterrell

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RE: Ion/vasimr tugs for non time critical cargo.
« Reply #4 on: 03/29/2008 08:11 PM »
Quote
Patchouli - 28/3/2008  4:00 PM

This engine claims to be 10x more efficient then smart 1's engine whch should give it an ISP of 27,000.

http://www.physorg.com/news9786.html

Even if it only proves to be twice as efficient in practice it will make a reusable tug very practical.


It can't be 10 times as efficient because ion engines are already about 50% efficient.

If it has 10 times the ISP, then it needs 1/10 the propellant, but 10 TIMES THE ENERGY. (OK, maybe 8 times if its 70% efficient).

That means it needs 8 times the solar power, or 8 times as long, or some combination of the two.

With electric propulsion you can have too high an ISP for a particular mission. For multi decade missions, the higher the better, but I suspect for LEO to LLO 4,000 will be about optimum.

(Ultimately, there will be a premium on a Variable Specific Impluse Rocket. Lets call it VASIMR for short)

Ultimately, I looked at Space Tugs but preferred momentum exchange tethers. See thread in Advanced Concepts.

Offline tnphysics

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Re: Ion/vasimr tugs for non time critical cargo.
« Reply #5 on: 03/30/2008 04:13 AM »
The same idea would give even more help to a Mars mission.

Note that for interplanetary missions SEP/NEP could REDUCE transit times vs. chemical, owing to there higher Isp allowing more delta-V. The drop could be as large as a factor of 2 while expanding abort options.

Offline Patchouli

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RE: Ion/vasimr tugs for non time critical cargo.
« Reply #6 on: 03/30/2008 04:49 AM »
You got a little confused I ment ISP by efficiency as for milinewtons per watt thats likely a little better but not 10x if anything it'll be the same if it's 50% still.

Not sure where you got the 10x number the dual stage ion engine might use a little more power as for pure hall thrusters I feel they may already be outdated.

If you move a given mass faster it has a bigger reaction then the same mass moved at a lower speed.

A bullet has a lot more kick then the reaction force of lets say a soft ball even though the soft ball is more massive.

The same charge that made the bullet go 2100ft/sec may only make the soft ball go 280ft/sec.

Really it just boils down to same energy is being put in the smaller amount of propellant making it able to do more work in producing thrust.

So the new engine may use about the same amount of power but uses less propellant the achieve a given level of thrust.

Though VASIMR is likely idea since it'll have less gravity losses and would not take a year to reach the moon.

Still I feel pure cargo should be banned from being able to use a chemical stage unless it's time critical.

Offline Patchouli

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Re: Ion/vasimr tugs for non time critical cargo.
« Reply #7 on: 03/30/2008 04:53 AM »
Heck it could cut the time in half or more.
It makes going to mars a seemingly impossible maybe even suicidal task become relatively easy.

Even easier then it was to reach the moon during the 60s.

Offline neviden

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RE: Ion/vasimr tugs for non time critical cargo.
« Reply #8 on: 03/30/2008 12:00 PM »
Quote
alexterrell - 29/3/2008  11:11 PM
If it has 10 times the ISP, then it needs 1/10 the propellant, but 10 TIMES THE ENERGY. (OK, maybe 8 times if its 70% efficient).

That means it needs 8 times the solar power, or 8 times as long, or some combination of the two.
Or.. you can add 8 times as much power as you would minimally need and have everythingÖ

Electric propulsion has a good thing going for it in that it isnít limited by the energy released in chemical reactions (up to 450 s) or the melting temperature of a reactor (up to 1000 s). If you can improve W/kg of your power plant you can reduce propellant supplies or time needed or any combination.

While NEPs arenít that good in that metric, they have other things that make them useful (like missions to outer planets). SEPs have few options to increase W/kg to 1000 or even more. Just put more power on them and you have good solution for inner solar system (Earth orbits, Moon, Mars, NEOs). When you need even more power, isp, delta-v, reduced time or dependability simply use more SEPs that would work together to move a single payload as one ship.

http://www.entechsolar.com/STAIF04.pdf

Offline meiza

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Re: Ion/vasimr tugs for non time critical cargo.
« Reply #9 on: 03/30/2008 02:50 PM »
Umm, the energy costs mass and expensive hardware. You end up with either lower payload fraction or lower acceleration.

Offline neviden

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RE: Ion/vasimr tugs for non time critical cargo.
« Reply #10 on: 03/30/2008 04:24 PM »
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meiza - 30/3/2008  4:50 PM
Umm, the energy costs mass and expensive hardware. You end up with either lower payload fraction or lower acceleration.
It does cost more in both the price of hardware and the mass, but since this is going to be reusable system you only need to pay for it and deliver it to LEO once.

Quote
A_M_Swallow - 28/3/2008  10:27 PM
More fuel is needed if the ferry is reusable.  The ferry could have been lifted off the Earth on a different Launch Vehicle.  This report estimates the SEP and solar arrays would have a mass of about 9.2 mT.
http://uk.wrs.yahoo.com/_ylt=A1f4cfiEU.1HOV0B.XpLBQx.;_ylu=X3oDMTE2dW5zM2pmBHNlYwNzcgRwb3MDMTIEY29sbwNpcmQEdnRpZANVSzA1MDFfNTAx/SIG=1235boedb/EXP=1206822148/**http%3A//www.entechsolar.com/SPRAT-XX-SLA-SEP.pdf
Ok, this is one proposed 600 KW SEP. IMLEO is 80 mT of which xenon propellant is 25 MT and the actual wings are only 2 MT. If you would increase the weight of the wings to 20 MT you would get 6 MW SEP that would be able to get to LLO either in tenth of the time required or would need drastically less propellant. If you increased isp from 2500 to 10000 s, you would cut propellant requirements by 4.

They even show this by showing how the tug would only need 34 days to return to LEO from LLO compared to 215 days for outbound trip. Itís simply underpowered to do what itís required of it (8 km/s delta-v) and therefore need that much more time when it starts in LEO.

Use 4 (or even more) SEPs like this as one system and you have good setup to first deliver Mars ship to HEO and then for a faster then chemical transit from HEO to Mars orbit and then back. You could even return with fewer working SEPs back to Earth, but it would take a little longer to do that.

Offline alexterrell

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RE: Ion/vasimr tugs for non time critical cargo.
« Reply #11 on: 03/30/2008 08:43 PM »
Quote
Patchouli - 29/3/2008  11:49 PM

You got a little confused I ment ISP by efficiency as for milinewtons per watt thats likely a little

Really it just boils down to same energy is being put in the smaller amount of propellant making it able to do more work in producing thrust.

So the new engine may use about the same amount of power but uses less propellant the achieve a given level of thrust.


Momentum = mass x velocity
Energy = 1/2 x mass x velocity^2.

If you throw out (a) 1 kg at 1km/s, you get the same effect as throwing out (b) 0.1kg at 10km/s. OK?

The energy in (a) is 1/2 x 1 x 1000^2 = 500KJ.
The energy in (b) is 1/2 x 0.1 x 10000^2 = 5,000KJ

(b) uses 1/10th the fuel, but 10 times the energy.

Effective use of VASIMR for short duration missions (<1 year) requires effective solar power sources.

Offline Lampyridae

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Re: Ion/vasimr tugs for non time critical cargo.
« Reply #12 on: 03/31/2008 05:37 AM »
With solar electric propulsion, it helps to think of power as well:

Pin = solar power from your arrays, typically 100W/kg for near-term advanced photovoltaics.
e = efficiency, i.e. how well the ion drive translates electrical power to jet power
Pout = aka jet power. This is nothing more than (exhaust velocity) x (thrust)

Here are some examples, both using a 100kW PV array.

Example 1 (scaled-up SMART-1):

Payload: 50 tonnes
Propellant: 20 tonnes
PV array: 10 tonnes (approx 100kW)
Ion drive: 20 tonnes
Isp: 1 600s
Thrust: 68N
Acceleration: 0.0068m/s^2 (pretty good for an ion drive)
Jet power:
Delta V: 4km/s
Time taken: 2 months

Example 2 (super-Isp performance 10x SMART-1)

Payload: 67.5 tonnes
Propellant: 2.5 tonnes
PV array: 10 tonnes (approx 100kW)
Ion drive: 20 tonnes
Isp: 16 000s
Thrust: 6.8N
Acceleration: 0.00068m/s^2 (still higher than SMART-1)
Jet power: 100kW
Delta V: 4km/s
Time taken: 20 months

Chemical EDS

Payload: 30 tonnes
Propellant: 60 tonnes
PV array: 0 tonne
J-2 + tankage: 10 tonnes?
Isp: 450s
Thrust: lots
Jet power: 50kW or more
Acceleration: about a G or so
Delta V: 4km/s
Time taken: 3 days

You can immediately see that the pacing item here is not the actual Isp of the drive, but the specific power (ie kW/kg) of the ion drive and solar panels. Note that I have left out very important things like radiators. A 50% efficient ion drive running off 100kW has 50kW of heat energy to get rid of.
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Offline neviden

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Re: Ion/vasimr tugs for non time critical cargo.
« Reply #13 on: 03/31/2008 07:11 PM »
Quote
Lampyridae - 31/3/2008  7:37 AM
Pin = solar power from your arrays, typically 100W/kg for near-term advanced photovoltaics.
I think that you are being too conservative. 300 - 500 (and even more) should be achievable. For easy comparison (http://www.entechsolar.com/SPRAT-XX-SLA-SEP.pdf):

Example 3 (SLA with direct drive Hall Xenon thruster)

Payload: 22 tonnes
Propellant: 25 tonnes
PV array: 2 tonnes (approx 500kW)
Ion drive: 7 tonnes
Isp: 2500s
Thrust: 29.4N
Jet power: 300kW
Delta V: 8km/s
Time taken: 8 months

More power would either speed up the trip or reduce propellant consumed.

Offline meiza

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Re: Ion/vasimr tugs for non time critical cargo.
« Reply #14 on: 03/31/2008 07:41 PM »
You need support and attitude changing structure as well as power conversion equipment for the solar cells. It's hard to get a light system. Look at ISS. The panels are very light and flexible and the trusses still mass a lot.

Offline A_M_Swallow

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Re: Ion/vasimr tugs for non time critical cargo.
« Reply #15 on: 04/01/2008 04:53 AM »
Quote
meiza - 31/3/2008  7:41 PM

You need support and attitude changing structure as well as power conversion equipment for the solar cells. It's hard to get a light system. Look at ISS. The panels are very light and flexible and the trusses still mass a lot.

In the above example that is probably why the dry SEP mass (Ion drive) was given as 7 mT.
Chemical fuel for the 5 mT lander was estimated as 18 mT.

Offline A_M_Swallow

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Re: Ion/vasimr tugs for non time critical cargo.
« Reply #16 on: 04/01/2008 04:59 AM »
Are the Model T-100 SPT Hall Thruster and Solar Array still in the vacuum chamber?  The plan showed that they had 6 more months to go.

Is the TacSat IV satellite with the new design of solar panels still due to be launched this year?

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