Author Topic: Cygnus as a space tug  (Read 6716 times)

Offline Jose

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Cygnus as a space tug
« on: 06/20/2012 04:42 PM »
Let's assume a hypothetical future with fuel depots and space stations at some Lagrange point. Wouldn't Orbital's Cygnus be a great platform for building space tugs to ferry people and cargo between LEO and the hypothetical stations?

It's modular Service Module (SM) plus Pressurized Cargo Module (PCM)  design gives it flexibility. You could maybe use the same SM on cargo-only versions that could ferry fuel and other necessities.

Also, doesn't the ISS heritage of the PCM make it suitable for extended stays in space?

Tryin' to show a little more interest here.



Online Robotbeat

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Re: Cygnus as a space tug
« Reply #1 on: 06/20/2012 06:21 PM »
A vehicle capable of aero braking (and perhaps also emergency Earth return for people) would be better if you're talking about reusable and round-trips.

If you're talking about one-way (with perhaps disposal) and cargo-only, then I would say emphatically yes! Cygnus would make a pretty great, lightweight vehicle for transporting a bunch of cargo to a Lagrange point. The enhanced Cygnus can get a whole bunch of cargo (has a pressurized volume of 27 m^3, but a dry mass of only 1800kg!) to a Lagrange point.

Heck, with micrometeorite protection (ala PMM), it might also provide a nice increase in living space for very little added mass, with much more room than an Orion spacecraft. The many advantages of a modular gateway...
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

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Offline vulture4

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Re: Cygnus as a space tug
« Reply #2 on: 06/30/2012 02:19 AM »
The space tug was one of the elements of the original Space Transportation System, or STS, back in the early 70's, along with the Shuttle and Station. It was to shuttle between the station and GEO or other remote orbits.

Offline pathfinder_01

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Re: Cygnus as a space tug
« Reply #3 on: 06/30/2012 02:57 AM »
Let's assume a hypothetical future with fuel depots and space stations at some Lagrange point. Wouldn't Orbital's Cygnus be a great platform for building space tugs to ferry people and cargo between LEO and the hypothetical stations?



Cargo yes, people no. A capsule or something capable of landing in an emergancy is a better option.  The mass of heat shields and landing systems isn't that bad. However I can see a heavily modified on taking on the role of the MMSEV.
« Last Edit: 06/30/2012 03:12 AM by pathfinder_01 »

Offline Jose

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Re: Cygnus as a space tug
« Reply #4 on: 06/30/2012 05:37 PM »
I was also assuming something like a space operations center as an endpoint for the tug.  But I take your point, what if the space tug couldn't rendezvous with the SOC for some reason? The ability to re-enter by itself would be awfully handy then.



Offline Danderman

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Re: Cygnus as a space tug
« Reply #5 on: 06/30/2012 07:33 PM »
Let's assume a hypothetical future with fuel depots and space stations at some Lagrange point. Wouldn't Orbital's Cygnus be a great platform for building space tugs to ferry people and cargo between LEO and the hypothetical stations?

Unfortunately not. Cygnus requires forward thrusters for control authority over it and its nose-mounted payload. Cygnus cannot simply mate with a payload and move it around, the payload must have forward thrusters that somehow join with the Cygnus prop system.

Offline A_M_Swallow

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Re: Cygnus as a space tug
« Reply #6 on: 07/02/2012 11:40 AM »
Unfortunately not. Cygnus requires forward thrusters for control authority over it and its nose-mounted payload. Cygnus cannot simply mate with a payload and move it around, the payload must have forward thrusters that somehow join with the Cygnus prop system.


For no more than say 20% of the development budget, can the Cygnus's cargo hold be removed and replaced by a section with forward thrusters and say a NDS docking port?

Offline Danderman

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Re: Cygnus as a space tug
« Reply #7 on: 07/02/2012 01:43 PM »
Unfortunately not. Cygnus requires forward thrusters for control authority over it and its nose-mounted payload. Cygnus cannot simply mate with a payload and move it around, the payload must have forward thrusters that somehow join with the Cygnus prop system.


For no more than say 20% of the development budget, can the Cygnus's cargo hold be removed and replaced by a section with forward thrusters and say a NDS docking port?

Probably, but that would not be  a useful space tug.

Offline A_M_Swallow

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Re: Cygnus as a space tug
« Reply #8 on: 07/02/2012 01:47 PM »
Unfortunately not. Cygnus requires forward thrusters for control authority over it and its nose-mounted payload. Cygnus cannot simply mate with a payload and move it around, the payload must have forward thrusters that somehow join with the Cygnus prop system.


For no more than say 20% of the development budget, can the Cygnus's cargo hold be removed and replaced by a section with forward thrusters and say a NDS docking port?

Probably, but that would not be  a useful space tug.


As a short range tug it will be able to push cargoes to where the ISS or EML spacestation's arm can grab them prior to berthing.

Offline Danderman

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Re: Cygnus as a space tug
« Reply #9 on: 07/02/2012 02:07 PM »
Unfortunately not. Cygnus requires forward thrusters for control authority over it and its nose-mounted payload. Cygnus cannot simply mate with a payload and move it around, the payload must have forward thrusters that somehow join with the Cygnus prop system.


For no more than say 20% of the development budget, can the Cygnus's cargo hold be removed and replaced by a section with forward thrusters and say a NDS docking port?

Probably, but that would not be  a useful space tug.


As a short range tug it will be able to push cargoes to where the ISS or EML spacestation's arm can grab them prior to berthing.

Nope. Without a forward thruster system connected to the Cygnus prop tanks, Cygnus does not have control authority for such cargoes.

Offline A_M_Swallow

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Re: Cygnus as a space tug
« Reply #10 on: 07/02/2012 05:27 PM »
Unfortunately not. Cygnus requires forward thrusters for control authority over it and its nose-mounted payload. Cygnus cannot simply mate with a payload and move it around, the payload must have forward thrusters that somehow join with the Cygnus prop system.


For no more than say 20% of the development budget, can the Cygnus's cargo hold be removed and replaced by a section with forward thrusters and say a NDS docking port?

Probably, but that would not be  a useful space tug.


As a short range tug it will be able to push cargoes to where the ISS or EML spacestation's arm can grab them prior to berthing.

Nope. Without a forward thruster system connected to the Cygnus prop tanks, Cygnus does not have control authority for such cargoes.


If you look back to my comments I suggested adding the forward thrusters.

Offline Danderman

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Re: Cygnus as a space tug
« Reply #11 on: 07/02/2012 05:32 PM »
If you look back to my comments I suggested adding the forward thrusters.

Its not clear from your comments if you mean adding forward thrusters to the front of the Cygnus bus, or to some sort of PCM (cargo module) or to the spacecraft that the Cygnus bus would push around.


Offline A_M_Swallow

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Re: Cygnus as a space tug
« Reply #12 on: 07/02/2012 05:39 PM »
If you look back to my comments I suggested adding the forward thrusters.

Its not clear from your comments if you mean adding forward thrusters to the front of the Cygnus bus, or to some sort of PCM (cargo module) or to the spacecraft that the Cygnus bus would push around.

Anything like that goes on the tug.  Keep the cargo module very simple.

A reusable tug could easily mode 10+ cargo modules in its life.

Offline pathfinder_01

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Re: Cygnus as a space tug
« Reply #13 on: 07/03/2012 03:03 AM »


Anything like that goes on the tug.  Keep the cargo module very simple.

A reusable tug could easily mode 10+ cargo modules in its life.

Why the intrest in a tug? ISS cargos can usually dock or get close enough to the station that they can be grabbed.

The Solar Panels for SEP could be large enough that they block docking or berthing but you could dock Cygnus to the SEP(or chemical rocket) then undock at your desination carring the cargo inside(or attached in the the unpressurized form) to it. Cygnus is pretty light it only masses like 1.5 or 1.8MT dry and carries 2.5 or 2.7MT worth of payload.

Offline pathfinder_01

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Re: Cygnus as a space tug
« Reply #14 on: 07/03/2012 05:21 AM »


No, ISS visiting *spacecraft* can dock or be captured and berthed, and those spacecraft can *carry* cargo. But *cargo* cannot do what you're suggesting.

However cargo can be placed inside a Cygnus or attached to the upressurized cargo module. Think of it as a wrapper.  What loose cargo would you launch on a rocket and use the rocket's thrusters to control it till the tug arrived? Maybe a spacestation module perhaps, but that could be delivered via rocket stage.
« Last Edit: 07/03/2012 05:23 AM by pathfinder_01 »

Offline A_M_Swallow

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Re: Cygnus as a space tug
« Reply #15 on: 07/03/2012 06:58 PM »


No, ISS visiting *spacecraft* can dock or be captured and berthed, and those spacecraft can *carry* cargo. But *cargo* cannot do what you're suggesting.

However cargo can be placed inside a Cygnus or attached to the upressurized cargo module. Think of it as a wrapper.  What loose cargo would you launch on a rocket and use the rocket's thrusters to control it till the tug arrived? Maybe a spacestation module perhaps, but that could be delivered via rocket stage.

An EELV can deliver say a 20 tonne module near to the ISS but does not have the highly accurate RCS needed to perform the docking.  A tug can be dispatched from the spacestation fly the say 5 miles to the module and dock with it.  The tug then pushed the module back to the spacestation and accurately places it ready for the berthing arm.

The module would only need expendable hardware for attitude control, despin control, a passive docking port and a location beeper.  All of which can be made fairly cheaply by using a standard design.

Offline Danderman

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Re: Cygnus as a space tug
« Reply #16 on: 07/04/2012 12:30 AM »
An EELV can deliver say a 20 tonne module near to the ISS but does not have the highly accurate RCS needed to perform the docking.  A tug can be dispatched from the spacestation fly the say 5 miles to the module and dock with it.  The tug then pushed the module back to the spacestation and accurately places it ready for the berthing arm.

The module would only need expendable hardware for attitude control, despin control, a passive docking port and a location beeper.  All of which can be made fairly cheaply by using a standard design.

The first paragraph describes an intermodal tug system perfectly.  I happen to hold the patent on this precise system.

The problem is that the Cygnus service module has significant problems in serving as such a tug. Its not an impossible job to modify it but most of the last few posts here defy the laws of physics.


Offline Danderman

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Re: Cygnus as a space tug
« Reply #17 on: 07/05/2012 04:47 AM »
and there was another thread about this last month:

http://forum.nasaspaceflight.com/index.php?topic=29151.0


Offline Jose

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Re: Cygnus as a space tug
« Reply #18 on: 07/05/2012 05:12 PM »
Dunno how I missed it. Lots of good info there, thanks!


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