Thursday, December 23, 2010

LEO-to-GEO Tug Part 1: Cheaper than a Delta-IV Heavy

Delta-IV Heavy
In response to recent blog posts about LEO tugs servicing Iridium’s satellite constellation, readers have been asking me about other uses for orbital tugs.

One tug use that keeps coming up in our discussions is a LEO to GEO transfer tug. Such a tug would pick up a payload in LEO and transfer the payload to GEO, drop the payload off in the correct orbit, and return to LEO for its next payload.

Although there are some intriguing propulsion technologies on the horizon that make the case for such a tug easier to close, could a transfer tug be developed today with today’ s propellants to serve the extreme ends of the GEO Satellite market (projected for the next decade to be 20-25 satellites per year)?  I focused my analysis on two GEO market segments:
  1. Smallsats (550kg) and 
  2. Mega ComSats (6,000-10,000kg)
So I did some analysis (yay, spreadsheets!).

With current propulsion, could a LEO to GEO transfer tug work for: 
  • SmallSats? NO, a LEO to GEO transfer tug could not be operated for less than the cost and performance of existing EELV rides
  • Mega ComSats? MAYBE: and the rest of this post discusses my analysis as to why an entrepreneur may find a market here.
Currently the largest GEO ComSat could theoretically have a mass of 6,276kg if launched on a Delta IV Heavy (correct me if I am missing a commercial rocket offering a larger BOL value for a GEO sat). I have heard of prices for this type of launcher ranging from $150-200M (maybe more). Since such a satellite in my example would push the boundaries of the capabilities of the Delta IV Heavy, I used the upper end price point of $200M to GEO.

I am assuming a commercial customer with a 6,276kg satellite could purchase a GEO ride on a Delta-IV Heavy for $200M. My analysis considered how to transport a 6,276kg satellite from the earth’s surface to GEO for less than $200M. 

The Falcon 9 has a LEO payload limit of 10,450kg.  My analysis assumes a Falcon 9 to launch the satellite to LEO and tug to take the satellite from LEO to GEO.  I considered two propellant options for the transfer tug:
  1. LOX/Kerosene at 340 ISP
  2. LOX/Hydrogen at 450 ISP
The table below shows the price comparison between the baselined Delta-IV and a Falcon 9/tug combo using both propellant options. 

The Falcon 9 & LOX/Hydrogen tug combo could deliver the satellite to GEO for only $142M (a cost savings of ~30%). The LOX/Kero tug at a lower ISP shows a cost savings of 6% (more if the launch costs end up being more than $200M). I am not sure 6% cost savings would overcome the risk of introducing a tug into the satellite-to-GEO equation, but 30% savings for the LOX/Hydrogen tug ($60M!!) seems pretty tempting.

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 as needed in LEO 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 (8% Market Share).
  • Operating Cost per year: $10M.
  • LEO to GEO: 4200 m/s of delta-v required.
  • GEO to LEO (with aerobraking): 1500 m/s of delta-v required.
  • Use aerobraking from GEO to LEO.
  • Satellite 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 GEO, could the tug make more money after dropping off its payload and prior to returning to LEO? Two thoughts:
  • Who would pay for prox-ops work in GEO?
  • What could the tug bring back from GEO to LEO (the delta-v to return to LEO from GEO is very low with aerobraking making return payloads comparatively cheap)? Who would pay to have a payload brought back?
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. The Delta-IV Heavy does not fly very often. This Falcon 9/Tug solution offers increased flight opportunities in addition to the cost savings already mentioned – frequent launch opps alone may make this venture valuable to customers.
5. Because SpaceX’s Falcon 9 becomes much more attractive for Mega ComSat operators when including a tug, SpaceX may be interested in being involved in a commercial tug venture.
6. There are going to be some elements of this analysis I get wrong. Assume I made mistakes. I welcome the corrections.

LOX/Kerosene Tug Details:

LOX/Hydrogen Tug Details:

Click here to play with the interactive spreadsheets.

In the next post in this series, I will walk through the math for a 10,000kg satellite to GEO (bigger than anything currently in GEO), and the numbers look even better – all from a Falcon 9 and a transfer tug!


  1. I've been thinking about this for a while. Some suggestions:

    - Comsats are typically dropped off in GTO and do the GEO insertion themselves
    - There exist relatively cheap 3.2km/s trajectories from LEO to L1/L2
    - L1/L2 <-> GEO stays outside most of the van Allen belts and is in almost continuous sunlight, which makes it perfect for SEP
    - From L1/L2 back to the surface is much cheaper than from GEO
    - Hypergolics may be good enough, especially with a pump-fed engine, which could give you storability, transferability and 340s Isp
    - LH2/H2O2 is an interesting propellant combination for a number of reasons:
    - Isp is fairly high (390s),
    - H2O2 can be used as a monopropellant for long duration,
    - H2O2 is storable
    - O/F ration is extremely high, which means you can launch all your oxidiser first and you only need to launch a tiny amount of LH2, which will fit easily even on a small RLV and this can be launched last (after the comsat and H2O2 both of which are storable)

  2. Great analysis! I always wondered about this option, and now you've fleshed it out.

    One of the big unknowns I have dealt with for my launch cost comparisons has been the current cost of the Delta IV Heavy. All I know for sure is that ULA has stated that they would price it at $300M once it has been upgraded to carry crew. I wonder if anyone knows of a public source for the current price?

    I have a Lagrange mission I'm fleshing out (some detail at the Open Space Organization website), and I use a LEO tug concept for some of the initial assembly - maybe I'll use your assumptions, since they look more detailed.

  3. Coastal Ron and Martjn:

    Both of you mention L1 missions. Stay tuned. Part 3 of this series considers the financial analysis for a LEO to L1 tug hauling a very interesting payload.

    Ron: I agree more exact pricing for the Delta-IV will be crucial for closing the business case. I too welcome anyone with more exact pricing.

    Martijn: I very much agree the type of propellant is a critical decision for any tug mission. the higher ISP of a LOX/Hydrogen is very attractive, but the added complexity of dealing with a dual propellant (cryos no less) should not be discounted. plus hydrogen is going to need much larger tanks due to its volume.

    The propellant debate is a healthy one.


  4. Yes, I think your first point is the key Martijn. The comparison should be between Delta IV Heavy to GTO vs Falcon 9 + Tug to GEO. That is: there is no comparison. Currently no-one provides GEO delivery. If someone was to start doing so they'd have an instant market, even if they cost more.

    Also, solar-electric propulsion isn't some "future" technology like VASIMR.. it exists today.

  5. Concerning L1/L2, I was still thinking of GEO as the final destination for the payload, but with the following unconventional route for the tug:

    Earth -> LEO chemical -> L1/L2 with LH2/H2O2 (3.2km/s) -> GEO by SEP (very cheap) -> L1/L2 by SEP (very cheap) -> Earth with H2O2 monopropellant (0.64km/s)

    You may want to split off the SEP parts onto a separate SEP tug, as this doesn't lend itself very well to reentry.

    This is an unconventional variant on the tug scenario, but I think the complications may be worth it, especially as an incremental stepping stone towards a LOX/LH2 tug. The main differences are that the tug would cycle back and forth from the ground (as opposed to LEO), take a detour in time and space, but save on delta-v. The result of this is that you can make do with TRL-9 technologies only.

    The benefit of H2O2/LH2 over LOX/LH2 (in the near term, not the long term) is that oxidiser is now storable while the extremely high O/F ratio (19:1!!!) avoids the problems with boil-off and low density of LH2, since you need so little of it. A tiny amount of LH2 would do and that doesn't take a lot of volume and since everything else is storable, it can go last so you don't have to worry about boil-off.

  6. Currently no-one provides GEO delivery. If someone was to start doing so they'd have an instant market, even if they cost more.

    There's probably a reason for that. I'm not sure what it is, but I imagine it is because launching to GEO with two stages is stretching it and having a separate third stage is not cost-effective compared to having a combined third stage/payload. On the other hand ESA/CNES/Arianespace have been studying GEO delivery for future Ariane derivatives.

  7. Another thought: the article is based around what you can do with a Falcon 9, but I think it may be more interesting to see what you can do with a Taurus II. The reason is that if you want to launch payload with two or more launches (either with a refuelable tug or with Constellation-style EOR) then your comsat is going to have to be able to survive in LEO for extended periods, something comsats are usually not designed for. This makes the sale harder, unless, like Orbital, you happen to sell comsats yourself. Taurus II is also smaller and therefore more in need of clever schemes to launch larger payloads.

  8. Orbital also has Cygnus/Dawn/DART expertise that would be useful for both a SEP tug and a chemical one.