> Sedna is expected to pass through the perihelion of its orbit in 2075--2076 and then move again away from the Sun. Considering the distances involved, a mission targeting the object would need to be launched "relatively" soon, especially if using conventional propulsion systems, which could require up to 30 years of deep-space travel.
Sedna's perihelion is ~76 AU - more than twice as far as Pluto, which took New Horizons nearly a decade to reach.
Sedna's apehelion is over 500 AU.
> The Direct Fusion Drive rocket engine is under development at Princeton
University Plasma Physics Laboratory
Is it ... is it actually working? How close are they? And even if they get it to work next year, will it be something well-engineered & reliable enough to send it into space for 10 years and expect it to work?
This direct fusion drive is a really interesting concept. Maybe something like this could be used for interstellar travel in a century (or five), it is very encouraging that there is active research on it. ~5kg of thrust is not a lot, but over time...
This sounds significantly more feasible than nuclear pulse propulsion ("project orion" style) which I used to think was the only feasible approach to get to another star.
One thing that was unclear from the paper to me: How does the fusion drive "pick" D/He3 fusion over D/D? Can this be "forced" by just cranking the plasma temperature way up? Or do you still just have to deal with a bunch of neutrons from undesired D/D fusion?
Very fascinating mission idea. Given how Sedna reaches so far away (>500AU), I wonder if the flyby would also reveal some details about conditions that distant. Maybe the surface contains some unexpected molecules that could shed light on its origin and what it's like that far out.
Already in orbit is OTP-2, which has 2 novel drive systems, one based on non-Newtonian thrusters, and the other based on an ION drive.[1]
Edit: The latter is "Fusion enhanced"[3]
The company’s the FireStar Drive uses is a water-fueled pulsed plasma thruster that uses a form of aneutronic nuclear fusion to boost its performance.
I watch the orbital observations closely to see if any altitude is being gained.[2] This is their second satellite in orbit, the first one had high voltage power supply issues so they never got to try the thruster.
I was surprised there were no references to past nuclear (fission) efforts, including a long test (more than 12.5 minutes) at 4000 megawatts of Pheobus 2A.[1]
Perhaps there are some solid or non-cryogenic liquid fuels that could take place of the liquid hydrogen and make fission based systems far more feasible in the near term.
Based on my experiences with Kerbal Space Program, this object seem to be almost being pushed off from solar orbit. Given its 'small' size, how much energy would be required to push it off the solar system?
Still a no-can-do for our species currently, and it's not close.
Would need around 1km/s on top of its average orbital velocity to escape, but the mass is probably roughly in the 10^22kg range, so thats like 10^28 Joule.
Significantly more than a billion of the biggest nuclear bombs we built.
Why dont they just launch a string of hundreds or thousands of tiny mesh probes out of a canon over a longer period of months or years? They dont need to be powerful if you have a big mesh network and each probe would only need to cost about what a cell phone does.
Cannon, not canon (the official texts, e.g. biblical canon, or Star Wars canon).
They don't launch space probes out of cannons because they don't make it out of the atmosphere. According to [1], muzzle velocity of a cannon is about 1685 ft/sec, which is 0.51 km/s. Delta-v to orbit is around 10 km/s. This is a feature, though, because launching your cannon shell into orbit means it isn't hitting it's target.
But let's suppose you have some propellant that is 20 times more potent. A cannon imparts all the energy at the beginning, with the acceleration happening as the expanding gasses push the projectile out of the tube. Assuming that the probe survives the initial explosion (unlikely), it is going to accelerate to 10 km/s very rapidly. Once calculation [2] put the g-force on a cannon shell to be 15 g, but lets say 10 g to be conservative. So we need 20 times more acceleration, so 200 g. Even if your probe is not smooshed in the acceleration, it is unlikely to be functional. (Note that, in comparison to cannons, rockets avoid this problem by providing the acceleration over a long period of time)
Now if you managed to engineer it for 200 g, air friction is going to burn it up. We know this because when spacecraft come down they have to lose all the velocity they got going up, and they tend to burn up. Heat shielding is almost certainly going to put you over the weight limit.
What, you say? This is a space cannon? Okay, well leaving aside how this cannon is going to burn the propellant without oxygen, the delta-v to Pluto from LEO is 8.2 km/s, so Sedna will be a little bit more. This is still an order of magnitude larger than the cannon, and still has acceleration problems. Plus, you had to use a rocket to get the payload to the cannon, so putting a second stage on the rocket.
You still have the issue that it's going to take a couple of decades to get there, which is what this paper is trying to address.
Those are valid points, and I appreciate you taking the time to make them. To clarify, when I misspelled "cannon" I just meant "big gun" rather than a literal piece of primitive weaponry.
More importantly, I would like to point out that while all of your concerns are valid, many of those problems were already solved in the 1960's. Project HARP[1] was able to use a 400 lb projectile to launch a 185 lb payload to a height of 111 miles... in 1966. We don't need anything close to 185 lbs of payload.
You'll note that 111 miles up is considered suborbital space. HARP was built mostly of 1950's era technology, and cost between $1000-$3000 per payload to fire. It had a 16" barrel and could be reloaded in about an hour. The payloads were encapsulated within a "sabot" to protect them, and the sabot seemed to do it's job, because primitive electronic instrument packages were deployed without being destroyed and weather balloons were deployed with success.
The long term plan for that project was to add a second stage which would push the payload into orbit, or beyond. There is no reason to believe it wouldn't have worked, but the Vietnam war happened and people lost the taste for funding space exploration. It was shut down. The enormous gun is still there, rusting where it was abandoned after firing nearly 100 ballistic payloads into suborbital space
Now, if we could fire ballistic payloads into suborbital space in 1966 what do you think we could achieve today? Honestly, the engineering isn't even that difficult, it's just a matter of figuring out how to pay for it. The rest is an incremental improvement over something we could already do in the 60's.
Sure, I'm glossing over a ton of minor issues (like the entire second stage), but those problems are also basically solved and we've learned a few things in the last 60 years. I not only think it's possible, I think someone should give it a shot (pun intended).
So I'm a fan of space exploration but this one seems... a reach.
First, you can't say that any of this propulsion tech is remotely mission-ready. It's all very speculative. There's been no real-world testing of any kind. You'd need to at least test-fire it in orbit and prove a solar sail in particular. Any kind of nuclear propulsion adds whole new levels of proof-of-solution (yes I know RTGs exist but those are technically quite simple being just radioactive decay rather than something utilizing fission or fusion).
Second, it's not clear what kind of speed this could reach. At New Horizons speed, assuming you can find the right launch window, you're looking at 18-25 years transit. That's a long time for a probe to survive.
If you do adopt a solar sail, what happens to it over 20+ years? What happens from long-term damage of hitting dust and micrometeors? Could you need to course corret if it gives uneven thrust?
And all this for... a flyby. Obviously Sedna is too far and too slow for anything else. Just like Pluto.
But if we're talking 2j0-30 year missions, I'd rather send an orbiter to Uranus. About 20 years is I believe the time frame for an orbital insertion to Uranus. IIRC Neptune is closer to 30.
16 comments
[ 3.3 ms ] story [ 42.2 ms ] threadSedna's perihelion is ~76 AU - more than twice as far as Pluto, which took New Horizons nearly a decade to reach.
Sedna's apehelion is over 500 AU.
> The Direct Fusion Drive rocket engine is under development at Princeton University Plasma Physics Laboratory
Is it ... is it actually working? How close are they? And even if they get it to work next year, will it be something well-engineered & reliable enough to send it into space for 10 years and expect it to work?
This sounds significantly more feasible than nuclear pulse propulsion ("project orion" style) which I used to think was the only feasible approach to get to another star.
One thing that was unclear from the paper to me: How does the fusion drive "pick" D/He3 fusion over D/D? Can this be "forced" by just cranking the plasma temperature way up? Or do you still just have to deal with a bunch of neutrons from undesired D/D fusion?
If the DFD takes 10 years to get there it means it would need to be launched in 40 years. That's quite a timeline.
Amazing that an organization can keep budgeting and planning for such a long project.
Edit: The latter is "Fusion enhanced"[3]
I watch the orbital observations closely to see if any altitude is being gained.[2] This is their second satellite in orbit, the first one had high voltage power supply issues so they never got to try the thruster.[1] https://www.nanosats.eu/sat/otp-2
[2] https://celestrak.org/NORAD/elements/graph-orbit-data.php?CA...
[3] https://www.aerospacetestinginternational.com/news/space/roc...
Perhaps there are some solid or non-cryogenic liquid fuels that could take place of the liquid hydrogen and make fission based systems far more feasible in the near term.
[1] https://en.wikipedia.org/wiki/Project_Rover#Phoebus
Would need around 1km/s on top of its average orbital velocity to escape, but the mass is probably roughly in the 10^22kg range, so thats like 10^28 Joule.
Significantly more than a billion of the biggest nuclear bombs we built.
They don't launch space probes out of cannons because they don't make it out of the atmosphere. According to [1], muzzle velocity of a cannon is about 1685 ft/sec, which is 0.51 km/s. Delta-v to orbit is around 10 km/s. This is a feature, though, because launching your cannon shell into orbit means it isn't hitting it's target.
But let's suppose you have some propellant that is 20 times more potent. A cannon imparts all the energy at the beginning, with the acceleration happening as the expanding gasses push the projectile out of the tube. Assuming that the probe survives the initial explosion (unlikely), it is going to accelerate to 10 km/s very rapidly. Once calculation [2] put the g-force on a cannon shell to be 15 g, but lets say 10 g to be conservative. So we need 20 times more acceleration, so 200 g. Even if your probe is not smooshed in the acceleration, it is unlikely to be functional. (Note that, in comparison to cannons, rockets avoid this problem by providing the acceleration over a long period of time)
Now if you managed to engineer it for 200 g, air friction is going to burn it up. We know this because when spacecraft come down they have to lose all the velocity they got going up, and they tend to burn up. Heat shielding is almost certainly going to put you over the weight limit.
What, you say? This is a space cannon? Okay, well leaving aside how this cannon is going to burn the propellant without oxygen, the delta-v to Pluto from LEO is 8.2 km/s, so Sedna will be a little bit more. This is still an order of magnitude larger than the cannon, and still has acceleration problems. Plus, you had to use a rocket to get the payload to the cannon, so putting a second stage on the rocket.
You still have the issue that it's going to take a couple of decades to get there, which is what this paper is trying to address.
[1] https://www.arc.id.au/CannonBallistics.html
[2] https://math.stackexchange.com/questions/3249185/calculate-g...
More importantly, I would like to point out that while all of your concerns are valid, many of those problems were already solved in the 1960's. Project HARP[1] was able to use a 400 lb projectile to launch a 185 lb payload to a height of 111 miles... in 1966. We don't need anything close to 185 lbs of payload.
You'll note that 111 miles up is considered suborbital space. HARP was built mostly of 1950's era technology, and cost between $1000-$3000 per payload to fire. It had a 16" barrel and could be reloaded in about an hour. The payloads were encapsulated within a "sabot" to protect them, and the sabot seemed to do it's job, because primitive electronic instrument packages were deployed without being destroyed and weather balloons were deployed with success.
The long term plan for that project was to add a second stage which would push the payload into orbit, or beyond. There is no reason to believe it wouldn't have worked, but the Vietnam war happened and people lost the taste for funding space exploration. It was shut down. The enormous gun is still there, rusting where it was abandoned after firing nearly 100 ballistic payloads into suborbital space
Now, if we could fire ballistic payloads into suborbital space in 1966 what do you think we could achieve today? Honestly, the engineering isn't even that difficult, it's just a matter of figuring out how to pay for it. The rest is an incremental improvement over something we could already do in the 60's.
Sure, I'm glossing over a ton of minor issues (like the entire second stage), but those problems are also basically solved and we've learned a few things in the last 60 years. I not only think it's possible, I think someone should give it a shot (pun intended).
[1] https://en.wikipedia.org/wiki/Project_HARP
First, you can't say that any of this propulsion tech is remotely mission-ready. It's all very speculative. There's been no real-world testing of any kind. You'd need to at least test-fire it in orbit and prove a solar sail in particular. Any kind of nuclear propulsion adds whole new levels of proof-of-solution (yes I know RTGs exist but those are technically quite simple being just radioactive decay rather than something utilizing fission or fusion).
Second, it's not clear what kind of speed this could reach. At New Horizons speed, assuming you can find the right launch window, you're looking at 18-25 years transit. That's a long time for a probe to survive.
If you do adopt a solar sail, what happens to it over 20+ years? What happens from long-term damage of hitting dust and micrometeors? Could you need to course corret if it gives uneven thrust?
And all this for... a flyby. Obviously Sedna is too far and too slow for anything else. Just like Pluto.
But if we're talking 2j0-30 year missions, I'd rather send an orbiter to Uranus. About 20 years is I believe the time frame for an orbital insertion to Uranus. IIRC Neptune is closer to 30.