Space Tug Or Not

[@darrellcherry9172]

I consider any vehicle that can reboost ISS is a space tug. It fits the definition.

[@EagerSpace]

I agree, though it gets a big complicated because they are also resupply vehicles.

[@shouryabose5943]

6:30 Satellite bus with tug characteristics

[@jeffbenton6183]

I think Mr. Deng would have a good laugh about that one

[@FourthRoot]

I would say a space tug is a module designed to rendezvous and alter the orbits of multiple spacecraft as its primary purpose.

[@donjones4719]

You make many good points, as usual. I crave accuracy and distinctness. Alas, I don't think it's a battle that can be won. Tug is a 3 letter word that's understood by everyone. Orbital transfer vehicle is >3 letters and requires the reader to know the concepts. Journalists tend to mostly use short words that the reader doesn't need to think about. Headline editors are ruthless about this. Everyday people say a pilot lands a plane on a carrier - despite no land being involved. Naval aviators say they trap on an aircraft carrier. Companies also prefer to use short terms, especially ones that are buzz words that make their product sound more capable or cutting edge than it is. I've tried to fight the terminology/accuracy/clarity problem on a couple of occasions and made no headway, the strong tendencies of language usage usually win out. Also, in my experience, in the cases of grey areas the simplest term that comes close to covering the subject gets used. The space tug problem has a number of grey areas.All of this applies to a varying extent even to the audiences of journalists who write about a variety of science subjects. Well, if we can't stem the tide perhaps we can divert it a bit.

[@LeonelEBD]

Well, guess that to this day the only space tug to have ever served was the Agena Target Vehicle as Gemini performed docking with it and changed its orbit using Agena's engine.

[@keilerbie7469]

The Superheavy booster is theoretically capable of SSTOing without a ship. Fly up one of those, refit it with 9 Rvac engines and NOW you have a real space tug.

[@dsdy1205]

Given its minimum thrust, good luck pushing any fragile payload that weighs less than Starship gently enough to survive the burn

[@keilerbie7469]

@@dsdy1205 9 Rvacs generate around 22.77MN thrust, a fully loaded superheavy (right now) weighs around 3500 tons fully loaded, that's a 0.663 T/W ratio, very survivable. The Falcon 9 upper stage routinely pulls 10 gees at the end of its burns. Not to mention the fact that with 9 engines you can actually throttle down even further by shutting down clusters of engines. An empty superheavy weighs around 200 tons, a single rvac firing at minimum thrust (40%) would give the empty booster a T/W ratio of 0.516... Not even 5m/s² of acceleration.

[@classic_sci_fi]

Satellite manufacturers would do well to standardize refueling ports or grappling points to accommodate space tugs.

[@debott4538]

I think this is a very good definition of a space tug. Rendevouz, dock, alter orbit. If we are feeling very fancy, I'd throw reusability into the mix: after mission complete, the tug returns to re-propellant for the next mission. Anything less would be a 'life-extension vehicle'.

[@EagerSpace]

I was thinking of adding that but it cuts down the field so much. Quark can maybe sort of do it sometimes if they are just moving the tug as they are using solar-electric propulsion, but I'm not clear on how the logistics work to get re-fueled - you need to get back to a specific orbit and have previously launched propellant to that orbit. I'm not clear that doing that is cheaper than just launching a second tug.

[@debott4538]

@@EagerSpace Yes, I agree. Totally fine with your definition. Re-tanking is still some time away. It might become cheaper when/if Starship tankers and/or lunar production go operational.

[@SirDeadPuppy]

nice vid whould love to see some more long form stuff

[@EagerSpace]

Thanks. The last two were topics I wanted to cover and they just ended up being a little shorter. I have some ones coming up that I *think* will be a bit longer.

[@rokadamlje5365]

Would the injection stage for say a lunar mission that got launched separately, be a tug? Somehow i think there should be a line between expendable stages and tugs.

[@EagerSpace]

I would argue no. Constellation called them "Earth Departure Stages"

[@atptourfan]

Really enjoyed this one. 😊

[@EagerSpace]

Thanks...

[@TheWizardGamez]

Blue origin and ULA lunar transfer and refuel vehicle qualifies. hope to see it fly some day.

[@thorin1045]

i would say the most important part of a space tug is that it does its job multiple times without landing. if it can dock with a satellite or other payload, change its orbit, undock and meet with a different one and repeat the process, it is a sapce tug (preferably with some way to refuel, so it does not have to be discarded when out of fuel.) if it only docks once or less, or boost only one vehicle, it is not a space tug. independent third stage, various boost stages and whatnot, including everything that was part of apollo is not space tug.

[@EagerSpace]

I considered that as part of my definition but thought it would be too limiting. The energy requirements of moving between orbits make it really hard to build a tug that can move even one thing and then get back to where it started, and of course that would reduce the payload it could carry.

[@thorin1045]

@@EagerSpace yep, it would be very hard (practically only the ion and nuclear type drives could do it). without more than one usage, it is just a booster. or the apollo command module was a space tug for the lander, which is not really something we usually called that.

[@chris_dixon]

Great video. Really enjoyed this.

[@Neront90]

Can spacecraft use main engines as cold thrusters? For example can Starship use its raptor engines with vector control to provide additional attitude contol using ullage gas or excessive fuel/oxidizer?

[@EagerSpace]

I don't think so. They do have the ability to prechill but I don't think there's enough control to do anything useful, and of course they only point in one direction.

[@1lustigermenschfighterlp458]

Alot of great videos lately, would a Starship tanker be a space tug, since it does rendezvous with a spacecraft but doesn´t change its orbit, albeit changing its orbit capabilities, count as a half space tug? Was the Shuttle a space tug for Hubble or the ISS, as it rendezvoused and changed its orbit?

[@debott4538]

I'd say Starship is more a 'tanker' in that example, and Shuttle was indeed doing tug activities.

[@donjones4719]

For the Hubble I think the Shuttle served as a freighter, it carried the cargo internally all the way from the ground. A tanker is a tanker, IMHO. By analogy to ships, even if it pushes the depot for a bit of orbit raising/maintaining it's not a tug - most ships inherently have the capability to tow. Ditto for the Shuttle doing orbit raising of the ISS. For a tugboat, moving another ship or barge is their primary role. I don't think half-a-space tug is a term that'll catch on.

[@1lustigermenschfighterlp458]

@@donjones4719 Yeah must have made a mistake, thought the Shuttle raised hubbles orbit by alot, same with the ISS bringing it to its current higher orbit in one mission but now I cannot find any information of that happening as I remembered :/

[@veedrac]

In my favoured flavour, if you start out in a full orbit, and you move to a different orbit, the component that did that was acting as a tug, regardless of whether that's its primary role or how it got there. If you make it about docking after orbit, that seems weird to me. Let's say it's something you have to fly separately on Falcon 9, but on Starship you can pre-dock it in the payload bay as part of a rideshare, because Starship is massive like that. It's still a spacecraft doing a tug in space, why would the definition hinge on that? A steelman I think is that it matters if it *could* rendezvous, but then I also think it's simpler to just take the Wikipedia option of saying it has to be separate from the launch vehicle in some way (several options are presented). But of course Wikipedia provides so many definitions because there is in fact no one true answer. A tug is whatever people call a tug.

[@mathiaslist6705]

Imagine some kind of hyperloop that accelerates an object in orbit by electricity. So around 400 m/s² or 40g of acceleration can give around 1.5 km/s at around 3 km or less than two miles. I don't know the efficiency of electric acceleration nor the exact power requirements. Just used E = 0.5 m v² as a rough estimate. It looks logical that acceleration without fuel or space infrastructure will play a role in the future.

[@EagerSpace]

See my video "Space Guns" for my view on that topic.

[@mathiaslist6705]

@@EagerSpace Unlikely you said something new but I might give it a try

[@PerigeeLIVE]

Love this video! IMO, a tug should be defined by being reusable, being able to integrate payloads on-orbit independently, and should preferably be LV-agnostic to get those payloads to them. A good example of this would be Cislunar Transporter.

[@PerigeeLIVE]

Concepts like the RS-30 hydrolox tug and the “nuclear shuttles” were all reusable as well. I think that should continue in the definition. A lot of these contenders can be judged on “is this basically a fregat.” Fregat is a great kick stage, but it doesn’t really do a lot else. We know it can be used as the base for a satellite bus, but we know it’s not a tug.

[@2150dalek]

I took the test...............I failed the test.📖🔍🐙

[@D_Rogers]

Does my T-Tug concept count as a space tug?? :D 🤞 I agree with the definition of a space tug being a craft that rendezvous with another craft for a period in order to change its orbit or destination. Have you seen some of the kooky NASA space tug ideas from the 1970s/80s? Profac (PROpulsive Fuel ACcumulator) was a nuclear-powered atmospheric scoop designed to collect oxygen from earth to be used as space tug propellant in an STS Space Transportation System to lunar bases! Who wouldn't want a bunch of reactors zipping overhead at astronomical speeds?? :)

[@chrissouthgate4554]

I feel that allowing journalists to define anything is a mistake. While they may have some language skills (but not always the case); They rarely have the subject matter training or background. This has been displayed over such a wide range of subjects & so frequently that I feel that caution should be used when letting them lose on long words & acronyms!

[@MARDLAMOCK]

did you look at a company called epic?

[@EagerSpace]

I limited myself to vehicles where somebody had called them a space tug, and I didn't find any references for them. I would call them "kick stage".

[@Astroponicist]

The ISS should not be deorbited. It should be a laboratory for on orbit recycling prior to on orbit equipment manufacture for on orbit use.

[@EagerSpace]

The problem is that orbital life is hard and many of the systems are not working well any more, and the risk to humans goes up. The Russians were willing to have a high risk station in Mir but that's not NASA's style...

[@Astroponicist]

@@EagerSpace NASA doesn't have to do the work, Russia is busy with Ukraine, & the ISS can be sold as scrap under an ISS termination agreement with the proceeds being divided amongst the original ISS agreement signatories. SpaceX can lift the contractors equipment to the proper orbit, & the work can be insured by Loyds of London. "In the case that a conjunction is found between two unmaneuverable space objects, each party is liable for the loss of their own satellite and for the debris created by it. It is worth noting that, according to Article IX23 of the Liability Convention together with Article VII of the Outer Space Treaty, states are liable for the dam- age caused by their non-governmental entities, which include private companies. Therefore, victims of damage cannot claim compensation directly from the satellite operator but the operator’s country." T. Wang

[@chengong388]

I have these tugs in KSP

[@g.f.martianshipyards9328]

I dream of nuclear-electric space tugs.

[@EagerSpace]

The problem with nuclear-electric is waste heat. You either need big and heavy radiators that push your empty mass up or you need to use high-temperature radiators with a gaseous coolant (hard to get enough flow) or something stupid like liquid sodium or lead.

[@g.f.martianshipyards9328]

@@EagerSpace That's why I used the word dream. Though I think these hurdles will eventually be surmountable.

[@Quasarnova1]

Shuttle Centaur is a space tug.

[@LeonelEBD]

I'd say no, it's just a kick stage 😅

[@Quasarnova1]

@LeonelEBD I agree, I just wanted to take the space tug claims to their logical conclusion.

[@ekowstevens4054]

A 'Tug' is British slang for something, well, erm, *cough*......Well good video as awlays.

[@tedarcher9120]

Space tugs have to be multi-use thp

[@TheWizardGamez]

Why is it easier to get to the moon that GEO????

[@EagerSpace]

Weird, isn't it? The problem is that if you launch from Cape Canaveral you have a lot of inclination in your orbit and it takes a lot of energy to get rid of it. If you want to go to the moon, the inclination doesn't matter and it takes less energy to get from GEO to the moon than it does to get rid of the inclination. That's only true for Cape Canaveral. Ariane launches from French Guyana and that location is only at 5 degrees inclination, so it takes them a lot less energy to flatten out their orbit. I *expect* that they can put more payload to GEO than TLI, but I couldn't find any figures to validate that.