Tuesday, December 28, 2010

LEO-to-GEO Tug Part 3: And Beyond...Bigelow to L1

In my FIRST post in this series, I discussed the benefits of a Falcon-tug architecture to transfer very large comsats from LEO to GEO (saving money over the Delta-IV Heavy price).

In  my SECOND post, I discussed the potential of a Falcon-tug architecture to carry a 10,000kg comsat to GEO (59% more payload than is currently possible on a Delta-IV Heavy).

In this, my THIRD post, I will discuss lagrange points

I do not intend to describe why one would use EML1, Rand Simberg and many others have posts on this topic if you are unconvinced.  Here is a Simberg lagrange post from 2006 in which he articulates several reasons to utilize EML1.  Instead, I will focus on the financials of such a mission. 

Using a Falcon 9/Transfer Tug architecture, what interesting payloads could you transport from LEO to EML1 (instead of GEO)? And at what cost?

The funny thing about orbital dynamics (which I am only a new student), if you can launch 10,000kg to GEO for the prices outlined in the previous posts, you can also launch 10,000kg to EML1 for even less.  Below is a visual of the Earth-Moon transportation energies (at Delta-V Scale).  It highlights how close GEO is to EML1 (and the moon for that matter) based on energy needed to get there.

Earth-Moon Transportation Energies at Delta-V Scale.
Used with permission from Brad Blair of the Colorado School of Mines.

Earth Moon Lagrange Point One (EML1) would make a interesting location for a space station and Bigelow’s Inflatable Sundancer module has a mass of 8,618kg – too large to be launched to L1 (or GEO) on an existing launcher (including Delta-IV Heavy) which top out a little over 6,000kg, but with the Falcon/tug transfer system described in these posts, a Bigelow Sundancer module could be launched from the earth's surface to EML1 for between $145-191M:

Since each station may consist of multiple Sundancer modules, some EML1 assembly may still be required.  But multiple missions to EML1 amortizes the fixed costs over more missions and could lower the price further.
Here are my Assumptions:
  • Tug is launched on Falcon 9 with a dry mass of 3,000kg.
  • Tug is co-manifested on a Falcon 9. Launch cost $20M.
  • Tug Development paid for under contract and not a part of this analysis.
  • Tug Manufacturing Costs: $50M.
  • Tug refuels itself in LEO as needed between missions from additional Falcon 9 launches (10,000 kg of prop for $50M: $5,000 per kg)
  • Tug lasts five years with amortization factored into price.
  • Tug breakeven price listed in this analysis.
  • Two missions per year assumed (but could be a mix of L1 and GEO missions).
  • Operating Cost per year: $10M.
  • LEO to EML1: 3800 m/s of delta-v required.
  • EML1 to LEO with aerobraking: 1000 m/s of delta-v required (Note: this link indicates the EML1 to LEO trip could be performed for as little 770m/s.  1000m/s has been used for conservatism).
  • Use aerobraking from L1 to LEO
  • Bigelow Sundancer launched to LEO on a Falcon 9.

1. Since propellant cost drives the price for this venture, true price reductions come not from increasing demand but from:
  • Decreasing propellant usage [could be solved through advances in engine technology (VASIMR)] or 
  • Paying less than $5,000 per KG for propellant [could be solved through extraterrestrial sources of propellant? Or SpaceX lowering their Falcon 9 prices due to added reusability in their first stage].
2. Once in EML1, could the tug make more money after dropping off its payload and prior to returning to LEO – what uses would you have for a tug in EML1?
  • By delivering the first Station to EML1, a market is created for resupply missions.  A separate analysis would need to be done on the best way to resupply this station, but a Falcon/tug scenario should definitely be one of the options to consider for the resupply missions as well
  • With L1's close proximity to the moon, what fun reasons could their be for diverting the tug occasionally (once in EML1) for lunar purposes.
3. Entrepreneurs reading this would want to calculate desired IRR to determine attractiveness of opportunity to investors. I have only considered a breakeven price.
4. Because SpaceX’s Falcon 9 becomes much more attractive for Comsat operators and for Bigelow when including a tug, SpaceX may be interested in being involved in a commercial tug venture.
5. There are going to be some elements of this analysis I get wrong. Assume I made mistakes. I welcome the corrections.

LOX/Kerosene Tug – Bigelow Sundancer to EML1 Details:

LOX/Hydrogen Tug – Bigelow Sundancer to EML1 Details:

Click here to play with the interactive spreadsheets for all three posts (in one file).

With these three posts I highlighted ways to launch comsats cheaper and larger than on a Delta IV-Heavy and to new and valuable destinations.  But LEO-to-GEO transfer tugs aren't the only way. 

One friend reviewing this analysis prior to posting was quick to mention the value of simply refueling the upper stages in LEO and bypassing the need for a LEO-to-GEO tug all-together (but needs a propellant depot instead). 

Which idea will blossom first?  The most profitable one (and the lucky one...but mostly profit).  Good luck entrepreneurs.


  1. LEO to L1/L2 is only 3.2 km/s if you take slow (>100 days) three body trajectories compared to the 3.8 km/s needed for a fast trajectory. That's a whole lot cheaper than GEO. And between GEO and L1/L2 you can use SEP without problems.

  2. Martijn:

    I might do quick relook at how cheap we could get the cost if the customer was more flexible with arrival date to L1.

    Since I built my analysis assuming only two tug missions per year, 100+ days to complete a single mission would be fine. Of course with increased demand, such “early adopter” discounts may not last long if demand grows.

    The opportunity cost of a new mission waiting in LEO would become too high for the tug to take the slow road. But in the early days, why not? Good point.


  3. Using Martijn’s suggestion of taking a slower. less propellant-intensive path to EML1 (3200m/s instead of 3800m/s for the outbound trip), the breakeven price points to deliver a Sundancer from the earth’s surface to EML1 look like this:

    LOX/Kerosene: $161M (16% savings over baseline)
    LOX/Hydrogen: $128M (12% savings over baseline)



  4. With SEP, transport between L1/L2 and GEO could be essentially free, apart from amortisation of the SEP tug which may not be negligible. On the other hand, there is no problem with the van Allens, so the SEP tug could be used many times which reduces amortisation costs compared to a LEO->GEO SEP tug which has to cross the van Allens repeatedly. The tug would also be in full sunlight all the time and the delta-v is relatively small, which helps round trip times and therefore also reduces amortisation costs. Return from L1/L2 to LEO (or the surface) is also much cheaper than from GEO (0.6km/s vs 1.4km/s).

    Without more detailed information about delta-v vs delta-t and power density of the SEP tug it is hard to be precise about the costs, but a detour through L1/L2 could turn out to be cheaper than launching straight to GEO. Especially if, like Orbital, you already have the components for a SEP tug lying around.

  5. Fast trajectories will be required for human transit missions to and from the Moon in order to minimize solar/cosmic radiation as well as cycling through concentrated Van Allen belt particles. These trips will need the higher delta-V Hohmann transfers (3.8km/s) and high-thrust systems provided by chemical propulsion. SEP and electrodynamic tethers are more suitable for cargo transfer.

    Two questions: (1) Have you considered the use of water as a shielding material for the L1 outpost? (2) Do your estimates include the mass for an aerobrake?

  6. Fast trajectories will be required for human missions in order to minimize solar / cosmic radiation and the number of cycles through the Van Allen belt

  7. The decreased performance thus higher consumption of kerosene (as compared with Hydrogen) may actually provide an economic incentive for a lunar ISRU plant dedicated to manufacturing liquid hydrocarbon propellants from polar ices that likely contain CO in addition to H2O. Tony Muscatello of Pioneer Astronautics demonstrated this could be done using the Fischer-Tropsch process.