Is FH really too big for comsats?

[john smith 19]

Judging by the expected huge payload hit stage reuse is taking I'd say "no."

This is a vehicle that's expected to have an expendable  payload to LEO of 53 tonnes.

Yet once you start factoring payload hits due to reuse you're down to what? 6 tonnes?

Staggering.

That said putting a 53 tonne tug up which stayed in orbit and handled the GTO process might make a lot of sense. the question would then be who would own (and develop) such a vehicle?

[Elmar Moelzer]

Yet once you start factoring payload hits due to reuse you're down to what? 6 tonnes?

6 tonnes to GTO

[Excession]

An appropriately-angled solar sail might offer some hope, but it's going to be a little complicated, especially if occasional passages through the earth's shadow need be factored in.  I think Robert Forward or Colin McInnes may have written something about this.

Using solar sails to create displaced orbits has been proposed and the dynamics worked out. It's very viable if you have a light enough solar sail.

[Llian Rhydderch]

Yet once you start factoring payload hits due to reuse you're down to what? 6 tonnes?

6 tonnes to GTO

So that seems to provide at least one answer to the original poster:

If SpaceX were to get the reusable parts of FH working, Falcon Heavy is not too big for commsats!

YMMV, and you can make different assumptions, in which case different answers might fall out.

[Adaptation]

It would take far too much fuel to 'hold' a satellite there, even with electric propulsion.  And a tether does not help, since the forces are towards the equator and would put the tether in compression, not tension. 

Using solar sails to create displaced orbits has been proposed and the dynamics worked out. It's very viable if you have a light enough solar sail.

Thanks I guess its sifi for now. 

Your question really belongs in Advanced Topics.

Sorry, the main subquestion of the tread was what could you do as a comsat with a bunch of extra mass, that was my idea on how to utilize it.

If instead of one satellite in the slot, you put (for example) 8, and space them out and let them all oscillate, then there would always be one north of the equator, one near the equator, and one south of the equator, though which one is in which position will switch.  This might be a sensible way to trade off satellite cost for increased capability.

Perhaps an elliptical constellation similar to what Sirius XM does could get by with fewer.  For terrestrial receivers a simple low cost parabolic based dish can be designed to receive a broad beam width in azimuth and a narrow one in elevation.  Would it be amicable to co launch a constellation like this on a FH or would the need for different insertion point consume too much delta-v?

[Lar]

Solar sails and "orbits" that don't go through the center of mass of the orbital system are off topic for this thread.  If someone can point me to a good topic area in Advanced concepts via PM I will move the posts prior to this note there. Posts after this note will be trimmed.

I love to go off topic but that's really FAR afield.

Edit: Trimmed one after this line I drew. I sent the text back to the author...   this time... Next time? maybe I will, maybe I won't. Why chance it! Find the right place so your nuggets of wisdom don't get lost for all eternity in the howling aether...

[john smith 19]

So that seems to provide at least one answer to the original poster:

If SpaceX were to get the reusable parts of FH working, Falcon Heavy is not too big for commsats!

YMMV, and you can make different assumptions, in which case different answers might fall out.

Yes.

Although I suspect the answer is highly counter intuitive to most people (well it was for me.    ).

[Ludus]

Everyone thinks FH is too big for comsats.  It can loft maybe 17t to GTO, and the biggest comsats are about 6-7t, so this seems to make sense.  Even Gwen Shotwell said "I'll talk very briefly about Falcon Heavy. So from a commercial perspective Falcon Heavy, it's an over-sized vehicle. It's got more capacity than folks in this room need".

But it seems to me only that the rocket is too big for comsats as they exist today.  If I was a comsat designer, and my boss came to me and told me they bought a FH, and is there anything I could do to make the satellite cheaper/more reliable/more capable with extra mass, I'd have lots of ideas.  Consider that a comsat now is about 6.5t with 4t of empty mass and 3.5t of fuel.  Some ideas might be:

- Drop the apogee motor entirely.   If the FH can put 17t into GTO, it can surely put 7t or so into GEO, assuming it can keep working for the 6 hours or so to reach apogee.  Then use Xenon for station keeping.  This gets rid of  tons of poisonous, sloshing liquid. making handling and testing easier and cheaper.  You can use the extra mass to make things cheaper and more reliable.

- Get rid of all the composites, beryllium, and other expensive materials.  Build it of aluminum.  Up the structural margins so you can eliminate a lot of painstaking design (to keep weight down) and inspection (if the margins are bigger, you can afford to miss small flaws).

- Double up on the solar panels, giving it twice what it needs.  Array deployment failures and solar cell degradation are two of the major failure modes.  This protects against both.

- Similarly, double up on reaction wheels, thrusters, or anything else that is remotely suspicious.

- Where possible, replace space-rated electronics with additional copies of merely mil-spec electronics.

And I'm sure there are many more ways to trade mass for cost or reliability.

Noting that two HS-702 satellites cost Thuraya a billion dollars ( http://space.skyrocket.de/doc_sat/hs-702.htm ), if you could make them for half the cost by letting them be twice as heavy, it would be well worthwhile to get an FH to launch them.

So from a systems life cycle cost viewpoint, it might well be that a FH is a better size, compared to a just-barely big enough rocket lofting a excruciatingly designed and tested satellite made of the finest unobtainium.

I think part of the OP's point goes way beyond the technical details of FH and FHR. It's that a large part of the enormous costs associated with comsats or indeed space hardware in general come from very limited payloads and enormous costs imposed by current launch vehicle technology. If reusability drives launch costs down by an order of magnitude or two, and SpaceX continues it's plans to build much larger launch vehicles that are also rapidly reusable, there are hundreds of ways to use that vastly larger mass budget to lower costs.

[AncientU]

At a recent Astro technology conference, I was discussing the display piece of an extremely light-weighted mirror (1.25m I believe).  The light weighting was 95%!  I asked how much would it cost if it was only light weighted 90% -- answer was 'half as much.'  This illustrates some of the potential when we back off of the bleeding edge of light-weighting.

[john smith 19]

I think part of the OP's point goes way beyond the technical details of FH and FHR. It's that a large part of the enormous costs associated with comsats or indeed space hardware in general come from very limited payloads and enormous costs imposed by current launch vehicle technology. If reusability drives launch costs down by an order of magnitude or two, and SpaceX continues it's plans to build much larger launch vehicles that are also rapidly reusable, there are hundreds of ways to use that vastly larger mass budget to lower costs.

I think you should add "recoverability" to that list.

Big life limiting failure modes for comm sats are a)Running out of station keeping fuel b)Loosing pointing accuracy.

Being able to therefor a)Refuel and b) Replace on orbit certain components would reduce satellite replacement costs quite substantially, but only if the sats can be brought back to LEO or serviced in GEO (and restored there). 

[Adaptation]

I think you should add "recoverability" to that list.

Big life limiting failure modes for comm sats are a)Running out of station keeping fuel b)Loosing pointing accuracy.

Being able to therefor a)Refuel and b) Replace on orbit certain components would reduce satellite replacement costs quite substantially, but only if the sats can be brought back to LEO or serviced in GEO (and restored there). 

The delta-v required by a service vehicle is non trivial.  Electric pulsive service unit could help.  I would think designs would have to be highly standardised and modular for this kind of repair to be practical, and it would be best with nearly universal adoption.  Given the state of ITAR restrictions I don't see this as something that could be american led effort.

[john smith 19]

The delta-v required by a service vehicle is non trivial.  Electric pulsive service unit could help.  I would think designs would have to be highly standardised and modular for this kind of repair to be practical, and it would be best with nearly universal adoption.  Given the state of ITAR restrictions I don't see this as something that could be american led effort.

Actually not as much as you might think.

NASA Goddard has been very active in the mechanical and electrical engineering needed to design "Orbital Replaceable Units" since the 1970's. Their biggest success was with Hubble where it's on orbit servicing missions have substantially extended its life. There are several conference proceedings on the subject.

Key features are a)Retainable fastners (so bolts don't float away) b)Restraining modules so they reliably interlock (that includes insuring electrical connectors are rigidly mounted (like computer boards going into a PC motherboard) rather than just a plug on the end of a bundle of wires, like a monitor cable.

Agreement is helpful but it's more a state of mind and the willingness to (possibly) add a bit of weight.

The simplest upgrade would be to allow in flight refueling (of either hypergols or Xenon) to extend lives.

Given the toxicity of hypergols I think current fittings are 2 part sealable IE when the join separates both ends seal off from the atmosphere. The trick is to put those connections on the outside of the sat, with some kind of docking markers.

I'd admit getting a comm sat with hypergol station keeping back to LEO is likely easier than ion thrusters as it can deliver a higher thrust kick, but I think it's possible with ion thrusters as well.

[Jim]

The delta-v required by a service vehicle is non trivial.  Electric pulsive service unit could help.  I would think designs would have to be highly standardised and modular for this kind of repair to be practical, and it would be best with nearly universal adoption.  Given the state of ITAR restrictions I don't see this as something that could be american led effort.

Actually not as much as you might think.

NASA Goddard has been very active in the mechanical and electrical engineering needed to design "Orbital Replaceable Units" since the 1970's. Their biggest success was with Hubble where it's on orbit servicing missions have substantially extended its life. There are several conference proceedings on the subject.

Key features are a)Retainable fastners (so bolts don't float away) b)Restraining modules so they reliably interlock (that includes insuring electrical connectors are rigidly mounted (like computer boards going into a PC motherboard) rather than just a plug on the end of a bundle of wires, like a monitor cable.

Agreement is helpful but it's more a state of mind and the willingness to (possibly) add a bit of weight.

It is a lot of weight since the spacecraft would have to be designed for orbital access vs weight and ease of terrestrial assembly.

Standardization is doable within a specific spacecraft manufacturer but not worldwide.  There isn't going to be a "universal" system. Just as car, planes and trains aren't. ITAR isn't the issue, it is corporate "secrets" and propriety information.  Refueling would be easier to do. 
Satellite are like computers, they have common subsystems (chips and boards) but not common enclosures and mounting methods.

[john smith 19]

It is a lot of weight since the spacecraft would have to be designed for orbital access vs weight and ease of terrestrial assembly.

I think that depends on how much of the satellite is designed for on orbit repair/upgrade. My instinct would be propellant, torque wheels and batteries. Provided the sat passes on orbit checkout torque wheels seem to be the big item.

Standardization is doable within a specific spacecraft manufacturer but not worldwide.  There isn't going to be a "universal" system. Just as car, planes and trains aren't. ITAR isn't the issue, it is corporate "secrets" and propriety information.  Refueling would be easier to do. 
Satellite are like computers, they have common subsystems (chips and boards) but not common enclosures and mounting methods.

I'd say a sizable part of the sections most likely to fail are on the bus side of most satellites so are likely to be quite standardized to begin with.
Actually given the high cost of space qualifying new parts I'd guess the range of parts used is quite small.

The real issue AFAIK is that satellites seem to be assembled with lots of wiring looms and plug/sockets which are no problem for humans but a royal PITA for robotic assembly/disassembly.

[Jim]

torque wheels

And they are usually buried in the spacecraft.

[Jim]

I'd say a sizable part of the sections most likely to fail are on the bus side of most satellites so are likely to be quite standardized to begin with.
Actually given the high cost of space qualifying new parts I'd guess the range of parts used is quite small.

The real issue AFAIK is that satellites seem to be assembled with lots of wiring looms and plug/sockets which are no problem for humans but a royal PITA for robotic assembly/disassembly.

No, like I said, they are contractor specific.   The buses are unique to each contractor.  And there are more than ten contractors/organizations in just the US   Most systems are installed on the basic structure of the vehicle or on inside of the exterior panels (using the outside as radiator).  And there are a lot of parts to chose from.

[LouScheffer]

torque wheels

And they are usually buried in the spacecraft.

On Kepler, at least, they were mounted on the outside of the structural panels, though probably covered with MLI.

http://spaceref.com/exoplanets/kepler-mission-manager-update-pointing-test.html