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The camera view from the Dart spacecraft

NASA’s DART spacecraft is destined for a head-on collision with an asteroid in the very first test of our planetary defence system.

Never say never. However, if we do already have Alien spacecrafts on Earth, we wouldn't be here sitting on our collective asses (no, I'm not going for the tired anal-probe joke) typing blissful comments on VS. We'd be long exterminated before we even notice them so they can take ownership of all of Earth's resources.

UFOs are real.
Alien spacecraft on earth are not.
The distances between stars make interstellar travel a pipe dream.

*promote go for launch

(edit)
Tour from Space: Inside the SpaceX Crew Dragon Spacecraft on Its Way to the Space Station

Come on NASA,

The shuttle and now the Orion spacecraft have been and are designed by congressmen and women for make work projects in their states.

The shuttle, although a marvel of engineering, was a death trap due to putting the most venerable structures down the stack.

ISS is a fantastic endeavour, but its low earth orbit and NASA has been struggling with a new direction for decades. The moon... no wait... asteroids... no wait... Mars... hold on... the moon.

Just PICK ONE, at least DOUBLE the funding to NASA and make whatever new project a national initiative. The American space industry can do unbelievable things when the proper foresight is put is place backed by money. (hay, maybe take some out of the military complex?!).

We will see if the Moon remains a target for NASA, maybe that will change when your current "leader" is removed... I am mean voted out of his "office".

Diagram of re-entry for the Soyuz:
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http://spaceflight101.com/soyuz-tma-20m/wp-content/uploads/sites/77/2016/09/6618866_orig.jpg

Orbital Module:
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It houses all the equipment that will not be needed for reentry, such as experiments, cameras or cargo. The module also contains a toilet, docking avionics and communications gear. Internal volume is 6 m³, living space 5 m³. On the latest Soyuz versions (since Soyuz TM), a small window was introduced, providing the crew with a forward view.

Service Module:
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It has a pressurized container shaped like a bulging can that contains systems for temperature control, electric power supply, long-range radio communications, radio telemetry, and instruments for orientation and control. A non-pressurized part of the service module (Propulsion compartment, AO) contains the main engine and a liquid-fuelled propulsion system for maneuvering in orbit and initiating the descent back to Earth. The ship also has a system of low-thrust engines for orientation, attached to the Intermediate compartment. Outside the service module are the sensors for the orientation system and the solar array, which is oriented towards the sun by rotating the ship.


Consequences of bad jettisons:
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The services modules are jettisoned before the spacecraft hits the atmosphere. A failure or partial jettison of the modules means that the capsule will not enter the atmosphere heat shield first which can lead to a number of scenarios:
- Capsule pushed off course (by hundreds of km)
- High sustained g-loads on reentry
- Plasma on reentry can burn through the craft if the heat shield is not exposed and oriented properly resulting in loss of crew.

https://en.wikipedia.org/wiki/Soyuz_5
https://en.wikipedia.org/wiki/Soyuz_TMA-10
https://en.wikipedia.org/wiki/Soyuz_TMA-10

It looks fun to me. Seriously, there are only two rides I have ever been on that I never went to go on again. The Twilight Zone ride, where it goes dark and you drop like 12 stories straight down or something like that. I screamed like a girl. 2: DMT breakthrough, a ride so far outside of this Universe that I screamed for my life louder and longer than I would like to admit, lol. After that, jumping out of a spacecraft back to Earth would be like floating in some soothing, calm Caribbean waters.

Since I quite enjoyed the talk I'm willing to overlook that fact He did also have some good examples of actual cold welding.

NASA has an interesting lessons learned article about the Galileo high gain antenna failure, which also seems to be more nuanced than "it was cold welding" - http://llis.nasa.gov/lesson/492

p.s. I got curious about the reference to Gemini, and I'm not 100% sure but I think it might come from a 1991 paper "On-Orbit Coldwelding Fact or Friction?" by Dursch, H. & Spear, S. (Bibliographic Code: 1991NASCP3134.1565D) or else it's from the paper it references as ref 5 (I. Stambler "Surface Effects in Space", Space/Aeronautics, Vol 45 No. 2, 1966 pp. 63-67).

That paper gives the opposite impression to the start of Derek's talk, rather than cold welding being discovered around the time of Gemini, it was often thought to be a problem around that time but as he says later was subsequently found to be quite rare (Dursch and Spear found no actual cases of cold welding causing spacecraft issues, they were usually friction issues due to fretting or galling caused by loss of lubricants, but still recommended taking precautions to avoid coldwelding).

It's not quite true to say it would take thousands of years to reach our nearest star. If only people weren't pussies about the small matter of exploding hundreds of nuclear bombs in the atmosphere, we could use technology that existed in the fifties to accelerate spacecraft to as much as a tenth of light speed. Proxima Centauri in a matter of decades, no problem.

There's no reason to actually do that; nothing to be learned, nothing to gain in terms of technology or resource exploitation or potential for the future, but god damn it, it would be cool.

A matter of scale, distance & speed. (assuming we are talking about electrically driven engines like ion drives or the proposed EM engine.)

If nothing else, the sun gets weaker the further away you get. Out at the edges of the solar system it's almost negligible.

Given that mass directly effects net thrust & fuel range, smaller craft working in the inner solar system may well be better off sticking with solar over a bulky reactor.

Larger and or longer ranged ships should start to favour fusion reactors and such.

Unless of course they manage to miniaturise the fusion apparatus, or perhaps harness quantum effects like matter/anti-matter. etc. etc.

Surface area to volume ratio also starts to shaft solar power the bigger the ship gets too. The panels would have to get exponentially bigger along with the ship/engines.

I couldn't tell you exactly where, but there will be natural tipping points between the practicality of one over the other.

Edit: The calculation would mostly be the ratio of energy produced to mass of the generating apparatus. The point where a fusion reactor (inc it's fuel) can produce more required power per unit of mass than solar cells (and associated gubbins), is the point where it becomes more efficient for most spacecraft.

Though solar still has a clear advantage where indefinite operational duration is a factor. (fusion requires fuel, albeit in small quantities)

Can you build a solar powered long-distance spacecraft? Or would fusion be better?

I love NdGT, but he's making a lot of assumptions here.

First he's comparing two fictional spacecraft, while knowing next to nothing about the relative strengths and weaknesses of their weapons systems, materials or engines.

It could be that phasers are to the Millennium Falcon what muskets are to a tank or vice versa.

Even then, Falcon v Enterprise isn't really an even match up. Maybe Falcon v runabout or Enterprise v Star Destroyer?

As for BB-8, how does he know that it's a smooth surface?

Finally, aliens might find kissing weird, or they might not. It's not even unique to one species on this planet, and it's almost certainly an evolved behavior. If aliens evolved on a similar planet, there's a chance they might evolve similar traits. Unlikely, but not impossible.

This spacecraft is about to start collecting regular data on the energy balance of the whole Earth - an important additional set of data on global warming. Of course the spacecraft was ready about 15 years ago - but Republicans did not want it to fly because (1) they hate Al Gore, and (2) they don't want us to know what they are doing to our planet. ("Close your eyes and vote Republican!")