Crew Tether Spin For Artificial Gravity On Way To ISS - Stunning New Videos - Space Show Webinar - Sunday
    By Robert Walker | May 23rd 2014 07:01 PM | 7 comments | Print | E-mail | Track Comments
    Following on from Crew Tether Spin - With Final Stage - On Routine Mission To ISS - First Human Test Of Artificial Gravity?, I've got some great videos to share now, showing the Soyuz and final stage spinning to create artificial gravity, over the turning Earth, against the stars. So, let's take a look at the highlights of the mission in video, ready for the Space Show webinar on artificial gravity.

    First, launch sequence, if you haven't seen it yet

    This shows how the final stage and the Soyuz end up in the same orbit - which is what makes this idea work

    Then, gentle tether spin just to keep the tether taught soon after separation of the Soyuz from final stage.

    All these videos are done in Orbiter, a remarkable space mission simulator by Dr. Martin Schweiger with lots of add ons contributed by enthusiasts.

    Thanks to Gattispilot, for making the tethers for these animations and for techy advice about how to attach everything together.

    That cube in the centre of the picture is just a visual indicator of the position of the c. of g. The real tether wouldn't have it.
    Reminder of how the mission works

    where all the boosts are done in Southern hemisphere, with the Soyuz moving in direction of orbit in its tether spin. The tether release happens in Northern hemisphere, a couple of days later - when the Soyuz is still a long way from the ISS and at a lower altitude.

    Main engine cut off just after launch

    Northern hemisphere 193 Km
    Southern Hemisphere 225 Km

    After spinup - about two days later

    Northern hemisphere 353 Km
    Southern Hemisphere 225 Km
    (all the boosts happen in Southern Hemisphere)

    Soyuz after tether release

    Northern hemisphere 353 Km
    Southern Hemisphere 278 Km
    (Release happens in Northern Hemisphere)

    Final stage after tether release

    Northern hemisphere 353 Km
    Southern Hemisphere 68 Km

    Uses hardly any fuel because the final stage ends up in an orbit with same semi-major axis - so with same gravitational potential energy - so all the energy from the boosts goes into the Soyuz on release of the tether.

    We have available, 15.7 m/second of delta v for the spinning. Tether can be any length but delta v has this as maximum.

    With a short enough tether this is enough for full g. Video of 100 m tether and 6 rpm

    This is 100 meter tether and 6 rpm, crew at 12.5 meters from tether centre of gravity - a spin rate that less susceptible individuals were able to withstand long term in rotating room experiments - taking one day to adapt after which they were symptom free.

    These were experiments using the rotating room facility of the Ashton Graybiel Spatial Orientation Laboratory at Brandeis University

    For details of these and other experiments see Theodore Hall's dissertation on artificial gravity.

    As it's just an add on experiment you wouldn't select the astronauts based on their susceptibility - but could certainly attempt to pre-adapt them with rotating rooms and pre-test them for susceptibility - and f it turned out that all the astronauts in the mission were low susceptibility and could withstand 6 rpm long term in rotating rooms on the Earth - it could be well worth a try.
    Or you can achieve 0.5 g at 50 meters and 3 rpm, total tether length of 200 meters.

    This is half g, same delta v - at 3 rpm many people might be expected to tolerate it long term with only mild symptoms, if the Earth experiments are a guide.

    So you could gradually let out the tether, once you achieve the required delta v - to try several different levels of Artificial gravity - for the same delta v. Using strong releasable tie-downs at, say, 50 meters for early experiments - then 100 meters, 200 meters, then 600 meters.

    Here is the final result when you have let out the tether completely, for lunar gravity 600m tether 1 rpm - Crew In Artificial Gravity Tether Spin

    Even most highly susceptible people have no problems with 1 rpm stays long term in rotating rooms on the Earth. So probably this would be fine for everyone in space also - that is if the Earth experiments are a reasonable guideline which nobody knows of course.
    Probably the crew would spend most of the mission doing this - though you could vary this from one mission to the other to get data for different regimes depending on what is of most interest for research etc.

    Finally then the tether release sends the Soyuz into higher orbit on its way to the ISS, with almost no loss of fuel over a standard mission - and sends the final stage to a targetted return to an empty part of the Pacific ocean.

    For many details, including:
    •  Motivation for the mission - the zero g health issues
    •  How you make sure it gets enough solar power during the spin
    • What happens if the tether gets broken by a micro-meteorite or space debris
    • How to be sure that the mission is safe for crew and for ISS no matter what happens to the tether

    see Crew Tether Spin - With Final Stage - On Routine Mission To ISS - First Human Test Of Artificial Gravity?

    That's also got links to the original paper, and lots of other references on artificial gravity and links to follow up.

    You can use the same method with any rocket launched mission with a final stage that goes into orbit.

    Same experiment with the Space-X Falcon 9 and Dragon when that's ready

    Similar ideas could also be used for lunar missions and interplanetary missions, because they also have final stages, and most of them send the final stage on an almost identical trajectory to the spacecraft itself - for practical reasons because the final stage of course has far more fuel than the spacecraft with conventional methods of propulsion

    (Indian MOM mission was an exception because of its use of gravity assist from Earth).


    Be sure to check out the webinar, this Sunday 25th of May. 1-3 PM PDT, (4-6 PM EDT, 3-5 PM CDT). I make that 8 - 10 PM GMT, or 9 - 11 pm BST. (website showing current local time in PDT)

    The webinar will be streamed from The SpaceShow on ustream.

    If you listen live, you can email questions to Joe Carroll - and other participants - and if you are in US or Canada and other places also, you can telephone the program and speak to him directly using a toll free number assigned to the Space Show, 1 (866) 687-7223

    For full details see the space show newsletter.

    If you can't watch it live not to worry, it gets archived soon after.

    Re-use of these videos

    I'm happy for anyone to share and re-use the videos in any way so long as they are attributed.

    The obvious thing is to release the videos on youtube under CC By which makes the videos available for anyone on youtube to mix and re-use as they like. However, youtube videos released under  CC By in that way can be used commercially. 

    Orbiter's license would permit that, and I'm okay with that myself -  but most of the add ons have no explicit license. So, I think you would need to ask the developers of all add ons used in the simulation to release it with that license.


    Joe Carroll doesn't say much about the use of a module at center of mass (CM), other than for microgravity experiments.

    - Wouldn't a module at CM be the only practical location for docking with other spacecrafts? Once docked, the payload could be transported along the tether to useful locations.

    - How would a rotating spacecraft be propulsed, if not by an engine at CM? Wouldn't offset engine locations change the rotation and attitude of the spacecraft, and not just its trajectory and speed as a whole?

    By taking full advantage of the CM, the spacecraft should not need to be spun down to microgravity for docking or propulsive operations.

    Also, I wonder what an EVA would be like on a rotating spacecraft! I suppose that the astronaut could stand on the "roof" of a module and would risk "falling off" along its sides.

    Okay - yes he did talk about this in the webinar, but can't remember when. You would have a counter rotating docking port for the spacecraft and yes they would dock at the centre hub.
    As for changing direction of the tether spin - first of all as he showed in the webinar - you can accelerate along the axis

    - but actually you can accelerate in any direction. If you have a counterweight which is a rocket engine, i.e. do the propulsion from the counterweight rather than from the hub or the crew habitat - then you can even arrange the accelerations of the rocket so that it continuously changes direction of the spacecraft while maintaining a constant full g inside the habitat throughout the maneuver. So basically you wouldn't even notice that anything is happening (unless paying particular attention to coriolis force perhaps).

    The key to this technique is to thrust askew of the centre of gravity of the system.

    See Method to Maintain Artificial Gravity during Transfer Maneuvers for Tethered Spacecraft

    Of course don't have to do that. Might be simpler to thrust from the c of g or even the crewed habitat, you'd feel the change in g, wouldn't be such an ultra smooth ride, but it would work fine.
    This is about techy details of the simulation.

    In summary it's reasonably accurate, the main differences are

    •  The Soyuz would probably be orientated with solar panels aligned radially - though the configuration shown here is also possible and is somewhat easier to set up.

    • The tether would be much brighter when seen from any distance to human eyes, bright as a bright star, indeed you would see it from the Earth in good seeing conditions when lit by the sun against a dark sky

    • I can't yet simulate tether release, wish I could. Orbiter could show video of both Soyuz and final stage, it all the way to the fiery burn up of the final stage in the atmosphere over the Pacific, and the Soyuz going into a higher orbit, but I don't yet know how to release the tether in a realistic way to achieve this.

    Orientation of Soyuz

    First - I show the space craft axially. It's easier to rig it this way, obviously just attach them together with the tether in same orientation they are in before they separate. But it's also possible to use other orientations.

    Joe Carroll's presentation will show a 3 leg bridle supporting the capsule sideways which has advantages. That's easier to do with the Soyuz than Dragon, because Soyuz has a fairing over the capsule itself, so the bridle doesn't need to be protected against ascent aero loads and heating.

    I did it as shown in the videos for techy reasons in Orbiter - it happened to make it very easy to get it into an accurate spin in the right direction and plane with the program. It is an "eyeballs out" configuration for the crew (terminology from Stapp's sled test days). Of course only under normal g or low g not hyper g but even so, not the most comfortable position for the crew.

    If I did it the other way, then it would take a lot of nudging of the attitude control jets and I'd only get it into an approximate orbit anyway. I'm new to Orbiter and not an experienced pilot of the vessels, rely mainly on auto-pilot.

    Brightness of tether

    The tether and spacecraft would be brighter when seen from a distance illuminated against the night sky by reflected sunlight. In Orbiter, zoom out far enough and the tether vanishes. 

    To get an idea of how bright they are, see this video of the NASA STS-75 being deployed, a very bright object from one mile distant.

    SEDS-2 was an easy naked eye object from the Earth.

    SEDS-2 viewed from Earth in 1994, surprisingly was an easy naked eye object, when front lit by the sun and viewed against a dark sky. It was just a few mm across.

    The reason it's so visible is because it's a bright object illuminated by the full brightness of the sun (far brighter than light reflected from the dark Moon) - so though it's tiny we still see it.

     Similarly stars would be way beyond our optical resolution, we wouldn't be able to see a single star from the Earth, if they weren't also so bright. A white object in space, reflecting most of the light of the sun, is going to be as bright as a sun-like star subtending same angle of view from the Earth. So even a tether a few mm across can be easy to spot from Earth.

    Actually any way of doing this would be an approximation - the human eye is sensitive to a far wider range of brightness than you can show within the limitation of the maximum of 256 brightness levels per pixel of a colour shown in a digital photograph or video or on a computer screen in the standard RGB byte format at varying brightness and fixed hue and saturation.

    The tether in these videos is 10 cm in width - the actual tether would probably be similar to a seat belt in width, 4.7 mm by 0.1 mm. If you make it wide, it has to be thinner for the same weight - and then is likely to fold up lengthwise under tension. But if it can be made 10 cm width and stiff enough, then that would further reduce chance of orbital debris severing it.

    Spectra tethers appear very white from the sunlit side, but they are translucent, so they are also visible when backlit. That let them track the SEDS-2 tether for much more of a pass.

    Simulating tether release in Orbiter

    I'd love to do this, but can't see an easy way to do it quite yet.

    The tether is actually a rigid body in these simulations - has same centre of gravity as a real tether - but it's not flexible. 

    Visually it looks the same, and physics of the assembly is the same while spinning. But the way it works at the moment, the tether and spacecraft are joined together using the "Attachment manager" in Orbiter. If I unattach them,it's not the same effect as releasing a tether.

    It would be quite techy to simulate the entire mission - doing burns at the right moment in spin and orbit - probably easiest with an auto pilot and I don't know how to do that.

    But might be easier to simulate just the tether release stage, get it all set up for the release, right orbit and spin rate delta v (accelerate to correct orbit first before spinning up, and just spin with a continuous burn until it's right spin rate - using double the fuel you would in the real mission).

    Then release tether at the apogee over Northern Hemisphere and show what happens next. That might need the flexible tether though. I'm investigating possibilities for simulating the tether release in Orbiter.

    Here is the webinar with Joe Carroll talking about tether experiments and his ideas for an Artificial Gravity Lab - now archived as video on vimeo:

    Partial and Artificial Gravity for Human Spaceflight 5-25-14 from The Space Show on Vimeo.

    and as audio here Broadcast 2249 (Special Edition)

    - linking to this article as background material for the show 
    Here's some info on space tethers. Part [5.2] lists the experiments made in space.

    This is photography of the two tethered satellites in the TiPS experiment mentioned above:

    I have a crazy spinoff idea from yours and Carrolls great ideas about artificial gravity:

    Could we add energy to a payload to be launched, by spinning it? The kinetic energy would then in space be converted to other forms such as electricity or heat. Or maybe most useful and simplest, to a change in trajectory by releasing part of the mass in the right direction as it spins very fast.

    Not only some dedicated wheel should be used for this purpose, but the entire payload should be spun. The mirror of a space telescope, the heat shield of a lander. The mass you'd need anyway would be "charged" with kinetic energy without adding any extra delta-V. Math I don't do would easily reveal if this could have any significance.

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