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Historical Spaceflight / Re: The Gemini paraglider / Rogallo Wing

« Last post by Blackstar on Today at 01:19 pm »

This is in a current aviation magazine in an article about the X-38. I don't remember seeing this time-lapse before.

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ISS Section / Re: 24/7 Livestream of Earth by Sen’s 4K video cameras on the ISS

« Last post by laszlo on Today at 01:09 pm »

I've been watching them for the last couple of days and it's magical - every time it gets to something I really care about the camera switches. How does it know? And what's with all the signal loss (again, usually just as an area I'm interested in is coming up)?

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SpaceX Starship Program / Re: StarCycler: A Starship-Based Artificial Gravity Station

« Last post by Paul451 on Today at 11:53 am »

Even if you have a solid hub, on a two-arm station you can't dock at the centre. Your docked-ship mass is poking out in the z-axis, and your station becomes dynamically unstable. (Classic intermediate axis instability.)

Does it become unstable? If 2 ships are rotating on long tethers isn't that the axis with most moment of inertia and therefore a stable rotation axis per classic intermediate axis instability?

Picture an object with three distinct dimensional axes, like a book. (Tennis racket is the usual example, but I find the rectangular shape of a book to be clearer.) There's a long axis, parallel with the spine. There's a short axis perpendicular with the cover. And an intermediate axis, side-to-side.

If you roll the book around its long axis, it is stable.(*) If you frisbee it around it's short axis, it is stable. But if you pancake-flip it around it's intermediate axis, it flips from side-to-side as it rotates end-over-end.

*(There's a type of long-axis instability. But you aren't going to see it with a book.)

During intermediate-axis rotation, it is still "stable" with it's end-over-end rotation, it will keep rotating that way as long as the momentum lasts, but you cannot prevent the unwanted side-to-side flip over. There's physically no way to throw the book around that axis, without it also rotating side-to-side.

(BTW: Really do this. Grab something with this shape and actually throw it around the three axes, see how two are stable and one is unstable. It's worth getting a feel for the difference. Imagine it was a rotating space-station, what that type of rotation would correspond to.)

Now picture a symmetrical stick (like a baton). There's still a long axis, down the length. But there's two identical short axes across the middle. There's no way to rotate it preferentially around one short axis.

Hence for a baton-style space-station (or tethered ships), a tiny shift in mass could push it from short-axis rotation to intermediate-axis rotation, because there's not enough difference between the short and intermediate axes.

With an actual baton or similar, you don't care if it's rolling side-to-side while flipping end-over-end. It doesn't matter. But with a space-station or similar, it is adding a whole extra type of unwanted rotation that will produce all kinds of weird forces inside the station, while also screwing up external alignments (like solar panel pointing). It might be enough force to break things.

But it's worse if you dock a ship at a mid-point hub. Now you've absolutely put it into intermediate axis rotation. So it will immediately be unstable, changing it's side-to-side orientation with each end-over-end rotation.

I am wondering if it does become unstable but due to a different issue with the center of rotation not being the centre of mass?

Centre of rotation will always be the centre of mass. I assume you mean the centre-of-rotation not being the geometric centre? That's not unstable. The two arms can have different masses and hence different lengths, and it will still happily rotation around the centre-of-mass.

Indeed, for an early station (or an ad-hoc "station" like two joined Starships), it can be used as an advantage. By having one heavy end, you increase the radius of the light end, increasing the centripetal gravity, which lets you experiment over greater g-levels at the same RPM.

Don't make the mistake of associating geometric symmetry with rotational stability, and asymmetry with instability.

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SpaceX Starship Program / Re: StarCycler: A Starship-Based Artificial Gravity Station

« Last post by crandles57 on Today at 10:55 am »

The problem with tethering is there's no hub to dock to.

No need for a hub.  The 2 ships just spin around their shared center of mass.  Thrusters adjust the spin rate.

How do you dock with that?

You can't anyway.

Even if you have a solid hub, on a two-arm station you can't dock at the centre. Your docked-ship mass is poking out in the z-axis, and your station becomes dynamically unstable. (Classic intermediate axis instability.)

Does it become unstable? If 2 ships are rotating on long tethers isn't that the axis with most moment of inertia and therefore a stable rotation axis per classic intermediate axis instability?

I am wondering if it does become unstable but due to a different issue with the center of rotation not being the centre of mass?

5

SpaceX Starship Program / Re: Risk acceptance/medical risk on human Starship to Mars, exploration / settlement

« Last post by Dave G on Today at 10:46 am »

For medical use a doctor is going to want an assistant that can help narrow down the symptoms (if needed), and then understand the possible solutions. That should be based on solid science, not word guessing, and it should be something that can be available by the time that Mars colonists leave Earth.

As for whether it "should be available by the time Mars colonists leave," maybe so, but if it's not available then that's certainly no show-stopper.

Yes, they'll want some adequate AI/ML algorithms on board when they leave earth, but this set of algorithms may be improved/expanded and sent to the crew during the mission.

Again, this is based on the information in the NASA link StraumliBlight provided, which seems to imply that the type of AI/ML algorithms used by the crew will be relatively small, not the huge AI models typically used in data centers.

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SpaceX Starship Program / Re: Starship Artemis Contract & Lunar Starship

« Last post by 321 on Today at 10:25 am »

Cool, lets do predictions.

SS will take more time and money than SX saying, but it will be done because so far Musk is not broke and show persistency.
And it will be a great success even if fist operational product will not be exactly what was planned in beginning (rapid reuse???), it will be a great success because of payload capacity, wide range of application and hopefully low cost.

Back to the topic, SS HLS in my opinion need at least another 4-5 years for demo landing in current form.

BTW, I would really love to see 2–3-time shorter SS HLS, to reduce complexity and risk of moon missions. No one really need 100t payload capacity, I guess 30-40t is plenty enough for foreseeable future.
 

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Chinese Launchers / Re: CZ-8 rideshare - Wenchang - February 27, 2022 (03:06 UTC)

« Last post by TheKutKu on Today at 10:17 am »

Taijing-3 01: China's first 0.5m resolution optical remote sensing satellite developed by a private enterprise. With a swath width of 12km and a total weight of 240kg, it carries a large-aperture optical camera, boasting high positioning accuracy and rapid on-orbit response. It can perform identity recognition, status recognition, and target detail recognition, producing vivid colors of ground features. Its panchromatic, near-infrared, and red-green-blue multispectral resolutions all reach top-level domestic standards. Taijing-3 01 was successfully launched on February 27, 2022, by a Long March-8 Y2 carrier rocket.

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Chinese Launchers / Re: Inaugural launch - CZ-12B - JSLC - NET(?) March or before late January

« Last post by TheKutKu on Today at 10:07 am »

Pictures

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General Discussion / Re: Orbitalradar – Explore Earth’s Orbits Live

« Last post by orbitalradar on Today at 10:02 am »

Just a quick update for anyone who tried the site recently and found it unavailable.

Orbitalradar was offline for a period due to a critical infrastructure failure. I’ve since rebuilt and restored the platform, and it’s now fully live again.

Thanks to those who reached out or checked back in, appreciate the patience. More updates to come as things settle back into a steady state.

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SpaceX Falcon Missions Section / Re: SpaceX F9 : Starlink group 11-30 : VSFB SLC-4E : 23 November 2025 (08:48 UTC)

« Last post by eeergo on Today at 09:18 am »

https://bsky.app/profile/planet4589.bsky.social/post/3mcnzlbnwzs25

According to the US Space Force TIP (Target Impact Prediction) the Starlink 35956 satellite, which suffered an internal failure on Dec 18 and generated as-yet-uncataloged debris, has reentered over N Queensland and Papua New Guinea at about 0713 UTC Jan 17