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.
Quote from: Danderman on 06/30/2012 07:33 pmUnfortunately 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?
Quote from: A_M_Swallow on 07/02/2012 11:40 amQuote from: Danderman on 06/30/2012 07:33 pmUnfortunately 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.
Quote from: Danderman on 07/02/2012 01:43 pmQuote from: A_M_Swallow on 07/02/2012 11:40 amQuote from: Danderman on 06/30/2012 07:33 pmUnfortunately 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.
Quote from: A_M_Swallow on 07/02/2012 01:47 pmQuote from: Danderman on 07/02/2012 01:43 pmQuote from: A_M_Swallow on 07/02/2012 11:40 amQuote from: Danderman on 06/30/2012 07:33 pmUnfortunately 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.
Quote from: A_M_Swallow on 07/02/2012 05:27 pmIf 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.
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.
Quote from: Jorge on 07/03/2012 04:41 amNo, 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.