Space Tugs

Whilst appauding the sentiments unless this is part of a new COTS program I don't think an OTV is in the budget. Let alone three! However with a minimal adaptation I think you will find that the ATV could be modified to act as a hypergolic powered tug. Otherwise you could ask the Russians to dust off their PAROM plans. The new paradigm means that America doesn't have to do everything.

A few points:

- first before we do anything new we need a common international docking system (ESA's IBDM might be a compromise here.)

-from what I understand there are no large payloads to be delivered on the American side. If something large was needed; could a Proton be used, docked to a port in the usual manner and then manipulated over to the American side?

- there are any number of reasons why connecting the ISS to a depot (of any sort) by a "long boom" is a bad idea, induced currents, venting, electromagnetic emissions... spring to this uneducated mind. No. Any depots would be best placed in a lower orbit and station kept by something clever in the way of an electrodynamic tether. One for LOX, one for Methane and one for Argon/Xenon. However I would suggest that there are at least two or three demonstrator missions required first before any useful depot technology could be deployed.

- hypergols are 'safe' in as much as they have been reliably used for ages. Some newer hypergols are even 'safer.' Lox and Methane storage and transfer are too full of unknown unknowns. Let's learn to walk with hypergols before we run with Lox/LCH.

-any Lox/LH depot is likely to be an ACES (Advanced Common Evolved Stage) derivative and its solar array is probably just for the electronics.

"Propellant loss rates in LEO are suppressed using passive TPS. The depot is designed to primarily boil-off and vent GH2 due to its factor of 10 higher thermal capacitance than GO2. This vent GH2 is used in LEO to satisfy the substantial station keeping requirements. Indeed with a well designed TPS the boil-off and station keeping needs are nearly balanced resulting in minimal loss."
http://www.ulalaunch.com/site/docs/publications/AffordableExplorationArchitecture2009.pdf

However let's see how CRYOTE pans out before we get too ahead of ourselves.

http://www.nasa.gov/pdf/458814main_FTD_CRYOGENICPropellantSTorageAndTransferMission.pdf

http://pdf.aiaa.org/preview/CDReadyMSPACE09_2074/PV2009_6440.pdf
Any advance on 2015?

As to the solutions:
1/ Jobs. Alas I can see no light at the end of the tunnel short of a crash program for which there is no money. Ground based R&D and small demonstration flights will have to come first.
2/ The only large module to be added to the ISS is Russian and they are using a Proton.
3/ An autonomous tug would not "demonstrate the current administration's intent to pursue human space operations." Only a manned Moon landing, say tomorrow would satisfy some folks round here!
4/ Both Progress and the ATV are capable of boosting the ISS. VASIMR is a very cheap way of boosting the ISS and (waves hands) should be operational well before any new OTV.

As to the rest: all well and good. However I don't think it's in the budget. Indeed I doubt if it is in the budgets for the other IPs.

However one surprising omission: SEPS or VASIMR tugs. If there is one technology that we really need to add to the transportation mix, it is the slow boat!

OASIS RASC Nailed it! The last thing we need is more Studies. Hopefully the 2011 budget will enable some Demonstrations!

He says: "The capacity of Atlas and Delta Heavy launchers can deliver about the same payloads to LEO, but they cannot directly deliver them to the station for either docking or unloading."

Can anyone explain to me what the problem is with Atlas V or Delta IV launching directly to ISS? I thought that the Falcon 9 and Taurus II will launch directly to ISS for COTS. Is figuring out a way to get a Delta IV Heavy launch to ISS really so hard? Couldn't it be done just with a service module like those used on Dragon or Cygnus?

I think we need tugs... but not in LEO. We need tugs to raise things assembled at the ISS up into higher orbits where they can be staged for use on Deep Space missions.

> Whilst appauding the sentiments unless this is part of a new COTS program I don't think an OTV is in the budget.

http://www.nasa.gov/pdf/458813main_FTD_AutomatedAutonomousRendezvousAndDockingVehicleOverview.pdf

I think the idea of tug is nothing more than a reusable service module, just like you say. Whether a reusable or disposable module is better is a matter for an engineering trade study.

However, my inclination is that something reusable on orbit is better in terms of long-term cost reduction. Add in that its something large enough it could keep people employed while focusing on practical aspects of a real orbital infrastructure makes for good engineering, workforce management, AND politics.

I really like this: constructive comments, actual ideas, and a focus on sustainable infrastructure development is what we need right now.

I don't see anything to recomend this approach. There is a OTV invisiged in the proposed 2011 budget, but it is a VASMIR space tug. for use from LEO to GEOS & lunar orbit if we ever need that.

The space tug discribed in this article simply extends the dying process for chemical rockets in space. Chemical rockets are for getting things into orbit from deep gravity wells. For doing anything in space, we need SEP/Ion/Plasma systems.

We need to carry the wonded but shoot the straglers. To space "Rockets". In space "Space Ships". Probably the way it needs to be. Anything that isn't in this critical path of
development needs to go away.

Ad Astra.

The ISS orbit isn't the best for supporting geosync satellite servicing. Doable, but I wonder if the there-and-back propellant overhead would be too high to support a business case for establishing such an infrastructure. Aerobraking and tether boosts would help, but the increased mass would factor in to tighten the margins, potentially too much...

Ditto missions beyond. Keeping things in the vincinity of the ecliptic brings along serious simplification and reduced propellant consumption.

Agree on the notion of using tethers to SK any propellant depots, but you'd want to send one up and down to keep the ISS at its desired micro-g state.

The first 'space tug' successfully boosted a crew into a higher orbit (enabling a rendezvous with another vehicle) back in 1966. It's about time we capitalize on the concept!

Great job, John!
You are to be commended for placing this idea on the table for discussion. Of course, had the space tug contained in the original Shuttle program been actually built (30+ yrs ago), we'd not be having this discussion...

A space tug is a very reasonable proposal for a new technology program, although I cannot agree with John on the cancellation of the Shuttle being a proper choice.

One important use of the tug proposed back in the 70's is for the deployment and retrieval of co-orbiting astronomical satellites, which could be serviced at the ISS then moved away to do observations outside the contaminated area around the ISS. Servicing the Hubble with single-purpose Shuttle missions has proven impractical.

An investment in tech development (as opposed to "operations" only) would allow a prototype that could test cryo (LOX/hyrocarbon) , storable (ethane/N2O or hypergol), and electric (i.e. VASIMIR) propulsion in one vehicle.

The Dragon, as well as the Prograss, ESA and Japanese supply vehicles have onboard single-use propulsion and nav systems for rendezvous with ISS but have limited payloads and cannot carry a single full-sized ISS module, though the latter would fit in a typical payload fairing, so the tug would allow much larger uploads as John says.

The Russians are building a crawl-through space tug that attaches to the ISS. Its dual-use purpose is to tug things around and serve as a manned habitat while not tugging. Denying this is going to happen reflects the resistance for the US government to take any first steps to make it happen and contributes to my talking points below.

You can also bet the US companies are going to compete with this concept to resupply the ISS and provide additional make-sense capability that effectively competes with what the Russians come up with or anyone else for that matter. Ironically, it takes a step in the right direction from foreign governments to set our government in the right direction. The Russians built cheap access to space, i.e., the Soyuz/Progress. Now, our government has woken up and is attempting the same thing since they do not want powerful and influential US citizens to access space in foreign or commercial vehicles without their approval.

It’s a simple matter of establishing the urgency in the minds of the buyers of such systems to spend the money to one-up one another in peaceful and healthy competitions that harms no one and puts a lot of people to work.

As far as having tugs in GEO, this is where the real money-making need is that does not involve government spending. GEO communication satellites make money by relaying data back to the ground to millions of users that pay $0.10/minute. They are built like Cadillacs to last as long as they can until some ridiculous anomaly occurs rendering the $250M money maker totally useless or out of control such as witnessed by the recent incident of an out-of-control satellite encroaching into someone else’s territory.

The other reason to tug GEO satellites around that the author, John Strickland, neglected to mention is when competition gets tough, and satellite TV dries up because of iPhones and causes leveraged communication businesses to go out-of-business because “This town ain’t big enough for the two of us!”, you simply move the satellite to a new town and expand the business worldwide.

Thanks for the link. Confirms my thoughts: three (four)demonstrator sats are all NASA can afford. Still whilst an OMV is not an OTV the synergy between it and a SEP stage may be worth a try. However it's way to go before this.

Or even this. Which are, I think, more in keeping with the intent of the original article.
Still baby steps...

If the tug is up in the 20 metric ton range then its propulsion unit can be a refuellable Centaur or Falcon 9 upper-stage. The docking arm and reconnaissance radar etc. would have to go up as 'payload'.