Catching Sedna

[Streetwind]

There's seemingly been renewed interest in interstellar missions in the past two years. Multiple organizations have declared it their goal to enable it by 2100, we have serious attempts at testing both solar electric propulsion and solar sails underway, and some people at NASA are not getting fired despite spending their time and budget on researching warp drives and quantum thrusters. Nevermind the flurry of exoplanet discoveries lately. And, of course, fusion power is only 20 years away, as we all know. Cough, cough.

Others have said this is madness, we haven't even gone manned beyond lunar orbit yet, and some of the most tantalizing locations in our own solar systems have yet to be probed. Several nations and agencies (and even commercial companies) have firm intents to visit Moon, Mars or both of them in the near future, both robotic and manned.

As for myself, I like to ponder the step in between.

Some of you may have heard of 90377 Sedna, a trans-neptunian object about half the size of Pluto. This means we're not talking about a comet or asteroid here, but rather a distant dwarf planet. Of which our sun seems to have a surprising amount of, largely courtesy of Neptune which seems to have gone bowling with all the elegance of a drunken elephant and shot well over 40 of these fellas way out there. But Sedna is a little special: it doesn't really come close enough to Neptune to have been bowled around by it. In fact, Sedna's perihelion is more than twice that of Neptune's aphelion, meaning that it's impossible for Sedna to come closer to Neptune than Neptune's maximum possible distance from the sun. Sedna's own aphelion, meanwhile, sits at a comfortable 937 AU. For those that don't immediately grasp this utterly mind-boggling number, here's an image showing Sedna's orbit compared to the rest of the solar system's planets (+Pluto).

This makes some people think that Sedna is not like the other dwarf planets and TNOs. They think it might be either a member of the Oort cloud - the only one we know of, so far - or that it was captured from interstellar space. Whatever it is, though, Sedna is thought to be one of the most scientifically valuable celestial objects currently known. What stories it might tell about its own origin and that of our solar system, we can only surmise. It bears tales from regions eight times as far from the sun as Voyager 1 has traveled... if not more.

Through an incredible stroke of luck, Sedna is currently falling towards perihelion at a pace that seems almost deliberately set up to still give us time. It will reach its "closest" point to the sun in 2076, at over 76.1 AU. Afterwards, it will swing out again, well beyond the Kuiper belt... and will not return to us for some 11,400 years. This is literally a singular chance that the cosmos is begging us to grasp. If we miss that window, we will either have ceased to exist as a species by the time of its return, or we will have evolved to the point where we can visit it at any point on its orbit at our leisure (albeit hundreds, if not thousands of years later).

With an orbit as eccentric as that, Sedna will be screaming past us some scant 62 years from now at close to solar escape velocity, out at twice the distance of Pluto's orbit. By that moment in time, we would already have to be out there for the rendezvous. There will be no second chance, ever. So the question is... can we catch Sedna? And if so, how would we do it?

Edited August 4, 2014 by Streetwind

[Horn Brain]

I think a New Horizons-style mission would be pretty easily within our grasp even now. Whip around Jupiter with a 20 year lead time and we'll be out there waiting for it to scream past. By the time we are ready to launch this mission, however, we will hopefully have some much more exciting options. Maybe we can send a nuclear electric driven craft out there with enough dv to actually orbit Sedna, or even bring a lander to examine the surface. The dv to return to Earth from Sedna would be something like 4 km/s - not actually too crazy when your Isp is 5000 s. I would think that a sample return would be a goal worth aiming for by this time. The mission wouldn't need to be much more dv intensive than the JIMO

[Streetwind]

Whew, and here I was beginning to think there would be no takers at all You'd think the KSP community would be more eager to ponder the details of such an unusual mission.

How would you go ahead and calculate the dV required to go from Earth to Sedna and burn into orbit there? I'd say that for a unique opportunity as this, and the effort potentially required, a mere flyby isn't really proper. Landing and sample return would of course be sweet, but that would greatly complicate the mission. Already there are a number of technical challenges to be solved:

- At that distance from the sun, solar power doesn't exist. And NASA has officially lost RTG manufacturing capability - in fact they're finishing up the Mars 2020 rover's RTG with a broken and damaged pellet press, keeping their fingers crossed that it doesn't fall apart before the last pellet comes out (else the Mars 2020 rover is toast). No replacement is in the budget anytime soon, and the project to develop a newer, better RTG type was canned for budget reasons many years ago.

- At the same time, we'll be pretty much limited to electric propulsion for Isp and tech readiness reasons, so we need electric power. It'll likely have to come from a small brayton cycle fission reactor like the one proposed for the JIMO. Which doesn't exist yet either. Thankfully there's some time yet before such a mission would need to be launched.

- If we're going nuclear, we have some interesting propulsion options in development right now: Ad Astra's VF-200 magnetoplasma rocket is rated at 5N thrust, 5,000s specific impulse at 200kW power consumption. It can also be set to deliver more Isp at the expense of lower thrust (but I don't know it's limits or scaling behavior). Another option in roughly the same power envelope would be ESA's dual-stage 4-grid ion thruster, expected to consume 250kW of power to offer 2.5N thrust at nearly 20,000 Isp (!). Both of these engines have been tested in the lab already (the DS4G in a downsized prototype variant) and will probably be flight ready by the time we need them - maybe even succeeded by newer variants.

- The systems on that probe would need to display Voyager levels of reliability, especially if there's a return planned in addition to the 20+ year one-way trip.

Still, I'd say that the need to create a fission reactor suitable for mounting on a spacecraft is one of the biggest hurdles right now.

[SuperFastJellyfish]

I wonder what you would see when you look towards the Sun from Sedna when it is ~550 AU away. That's the theorized focal point for using the sun as a gravitational lensing telescope using the gravitational lensing effect.

On a related note of an upcoming gravitational lensing event:

http://www.astrobio.net/topic/solar-system/meteoritescomets-and-asteroids/rare-stellar-alignment-helps-in-hunt-for-planets/

'The red dwarf Proxima Centauri, our sun’s nearest neighbor is heading for a rare conjunction with two distant background stars. First, Proxima Centauri will pass nearly in front of a 20th-magnitude star in October 2014. In 2016, the red dwarf will pass a 19.5-magnitude star. The alignment will allow astronomers to look for small planets orbiting close to Proxima Centauri. It will also provide data to precisely determine the mass of our nearest stellar neighbor.'

[indroth]

Not knowing the mass of Sedna makes anything beyond a flyby a difficult proposition at best. An impactor would be possible, and maybe orbit if there is lots of spare delta-v.

[Streetwind]

You can put upper bounds on the mass when you know the size. Of course that measurement too is imprecise, but it's definitely a lot smaller than Pluto. Most say that it's about half as big. So mass, and therefore gravity, is exceedingly unlikely to be larger than Pluto's.

It's basically about how much dV you're willing to throw at it versus keeping your spacecraft small and affordable.

[indroth]

It's basically about how much dV you're willing to throw at it versus keeping your spacecraft small and affordable.

Yes, I suppose it is mostly a cost vs risk issue. Aiming for something that has the delta-v and TWR to land on Pluto may be the way to go. If it isn't good enough, we still have an impactor .

[christok]

- At that distance from the sun, solar power doesn't exist. And NASA has officially lost RTG manufacturing capability - in fact they're finishing up the Mars 2020 rover's RTG with a broken and damaged pellet press, keeping their fingers crossed that it doesn't fall apart before the last pellet comes out (else the Mars 2020 rover is toast). No replacement is in the budget anytime soon, and the project to develop a newer, better RTG type was canned for budget reasons many years ago.

New Pu-238 production was approved in 2009 but there have been some budgetary delays.

NASA had a bit of a disagreement with the congressional subcommittee overseeing the DOE budget recently, because the DOE subcommittee wants NASA to pay every single cost related to restarting Pu-238 production for spacecraft (it used to piggy-back off nuclear weapons production) while the military routinely gets to order whatever they want whenever they want and only pays production costs. It ended in "NASA will pay". (http://www.planetary.org/explore/the-planetary-report/tpr-2013-3-polygons-on-mars.html)

Under these circumstances, I don't think it's fair to say that RTG manufacturing capability is "lost". There's just not enough Pu-238 to go around and there will probably be some amount of maintenance deferred.

[Sirrobert]

When would we have to launch in order to be able to randevous with it?

I imagine you'd need a few gravity assists to get out there properly, and you'd have to be at the right spot at the right time to. So how would the phase angles look?

[Chris P. Bacon]

Somebody needs to go in and add this sucker to RSS, so we can fast forward 20 years and work this mission out.

http://xkcd.com/1244/

[SuperFastJellyfish]

A quick google search found me this comment on this website that goes through some rough numbers for a Sedna mission. Whether they are sound, I do not know.

First order analysis

Given that we have practical ion thrusters, it's time to look at them.

Deep Space 1

The DS1 probe massed 387kg, had 83kg of fuel, operated for 162 days, and generated 92mN. So, it generated about 0.2mm/s^2.

The craft is not tanks-dry, either. It has approximately 6 months (180 days) of fuel per design. That's a roughly 20% fuel design, and my estimate on the mass of the thruster itself is 10kg - about 0.01N per kg, and linearly scaling, with about 16x thruster mass in fuel per year. (These numbers are rough, but provide a baseline)

Powering a 2 kW thruster...

In the inner solar system, solar power is viable for an electric thruster; out past the asteroids, it becomes pretty much non-viable.

Radio-thermal generators, likewise, are measured in kilograms per watt... one of the most efficient was on the voyagers, at around 40W of electricity out per kilogram... to get a reasonable 0.2mm/s^2 acceleration, they become impractical.

Which pushes us into the range of nuclear fission reactors. Which also means large masses - the SNAP-10A was 290kg and 30kW.

Into the hypothesizing

We need a multi-ton spacecraft. There is a design for a 100kW Electrical output, ~520kg nuclear reactor. This would be adequate to power 50-some NSTAR units at 91mN each; assuming only 20 such units, and 80kg each per 6 months in reaction mass, and 10kg each, plus a 200kg science payload, we can get a good first order hypothesis. I will assume for now a 5 year plant duration, since the SAFE400 has been in testing for several years, and I cannot find documentation for its fuel use.

kg kW Item

200 40 NSTAR x20, giving 2N

520 (100) SAFE-400 400kW/100kWe nuclear reactor.

6400 0 2 years NSTAR fuel for 20 units.

200 10 science package comparable to a mars orbiter.

7400 -- mission mass.

This would give a mission thrust at launch of 0.00027m/s^2. Almost directly comparable to DS1... and a 720 day thrust, using a turn and flip, is roughly 3.4 AU covered, and peak speed of 8.3km/s, or 17861396s per AU or about 209 days per AU ... and 71 AU to cover. This would mean about 41 additional years.

However, the actual acceleration would increase over the mission, and the mass of fuel being the largest proportion, we can use the average mass of around 4000kg for figuring overall - nearly doubling the engine-off speed, and cutting the coast time to about 20 years. The remaining issues are fuel for the power plant, which I lack the data to calculate.

A larger fuel mass could be used, increasing duration, but decreasing initial acceleration. A 4 year fuel duration, for example,

kg kW Item

200 40 NSTAR x20, giving 2N

520 (100) SAFE-400 400kW/100kWe nuclear reactor.

12800 0 2 years NSTAR fuel for 20 units.

200 10 science package comparable to a mars orbiter.

21800 -- mission mass. (probably about 1050kg tanks dry)

Initial would be about 0.00009m/s^2, with a peak of about 0.0019m/s^2, and an average of about 0.001m/s^2... and would cover about 51 AU under thrust, and peak velocity of about 62km/s... or about 28 days per AU, for about 2 years coasting time.

This would put a rough mission travel time on the order of 6 years, and about 1/2 of it thrusting outbound, 1/3 coasting, and 1/6 decelerating into orbit.

Unfortunately, the technologies are not all fully proven. By not fully proven, I mean (1) we don't know that they actually will survive a 4-year constant "burn"... tho' we know they will last at least 160 days, and (2) the fission system hasn't been in existence long enough to establish that it will in fact last the 4-10 years needed for a mission

Speculative answer

Yes, a first order analysis indicates it is plausible that a mission could be made, and with a flight time of under 10 years.

There are a number of vagaries, however, in the available data. Structural mass is simply estimated; fuel mass may be insufficient for the indicated duration, etc.

http://en.wikipedia.org/wiki/Radioisotope_thermoelectric_generator

http://solarsystem.nasa.gov/missions/profile.cfm?MCode=DS1&Display=ReadMore

http://en.wikipedia.org/wiki/Deep_Space_1

http://nmp.nasa.gov/ds1/

http://www.world-nuclear.org/info/Non-Power-Nuclear-Applications/Transport/Nuclear-Reactors-for-Space/

http://members.shaw.ca/bru_b/index/nkmoslikfly2.htm

http://web.archive.org/web/20050321055406/http://www.spacetransportation.com/ast/presentations/7b_vandy.pdf

[Streetwind]

When would we have to launch in order to be able to randevous with it?

I imagine you'd need a few gravity assists to get out there properly, and you'd have to be at the right spot at the right time to. So how would the phase angles look?

That's one of the questions I had in mind when making this thread. I'm unfortunately too much of an amateur to calculate phase angles, transfer times and dV costs by hand

However, considering how much larger Sedna's orbit is than that of earth, it would be fairly trivial to find a suitable launch window. Earth simply goes around the sun so fast that Sedna barely moves in comparison. It's like launching towards Jool... from Moho. Regardless where Jool currently is, you just need to wait a couple days until Moho is positioned properly.

In a similar vein, it's probably not too hard to find a useful gravity assist to sling the spacecraft further out. We brought spacecraft to solar escape velocity with gravity slingshots before (the Voyagers, as I'm sure I don't need to mention). It's just a question whether or not these slingshots will increase the total travel time. While saving dV is always good, this mission will likely be limited by lifetime of components, especially power generation.

A quick google search found me this comment on this website that goes through some rough numbers for a Sedna mission. Whether they are sound, I do not know.

That's actually a pretty cool find, great job!

So basically, a 3,000s Isp class electric engine (or cluster thereof) powered by a SAFE-400 fission reactor could conceivably pull off a six-year intercept with a 200 kg science payload... Okay, it probably won't work out to that in space, since the first order approximation assumes flying in a straight line, which is obviously silly in space. But hey, even if it took twice as long, it should have the dV to make it - provided the reactor lives long enough. This isn't bad at all.

As mentioned before in post #3, we nowadays have propulsion technology significantly better than needing a 20-cluster for 2N of thrust at 3,000s Isp costing 40kW. Both the VASIMR and the DS4G blow these figures out of the water (although they require quite a bit more power). So giving it a couple extra decades of electric propulsion advances would more or less guarantee that propulsion technology is a non-issue. We could likely even do a realworld 6 year intercept by brute forcing it with whatever we have available then. This bodes well for larger science payloads and even for sample return. Heck, it might even allow for two missions - first a probe arriving a few years before perihelion, and then a return capable lander launched shortly after the probe arrival and itself arriving a few years after perihelion. An extra AU or two isn't going to break the bank if you can hit it that fast.

That leaves once again the reactor as the prime unknown, as I suspected. The SAFE-400 itself is too small (100kW) for a VASIMR (200kW) or DS4G (250kW), but a 1200 class variant (or a trio of 400's) should manage. Of course, that is 1.5 tons in reactor mass alone. Perfectly doable with the higher thust and Isp of the mentioned engines, but not entirely ideal. Additionally, the SAFE project isn't even all that serious (it's done on the side with leftover funds and volunteer hours of that particular lab). And then there's the concerns of lifetime, which I know nothing about. This just shows that we really need a more serious look into power production for deep space missions in the coming decades.

Edited August 6, 2014 by Streetwind

[indroth]

However, considering how much larger Sedna's orbit is than that of earth, it would be fairly trivial to find a suitable launch window. Earth simply goes around the sun so fast that Sedna barely moves in comparison. It's like launching towards Jool... from Moho. Regardless where Jool currently is, you just need to wait a couple days until Moho is positioned properly.

Except that this will not be a Hohmann transfer. That would take around 120 years. If you look at the New Horizons trajectory, you will see that it is almost a straight line to Pluto intercept after the Jupiter assist.

Initial would be about 0.00009m/s^2

This is much less than the acceleration due to the Sun's gravity even at Jupiter orbit, so this second 6 year estimate is probably way off. I haven't tried figuring out how the spiraling trajectory that you get by burning prograde works out though.

[indroth]

Going off some of the performance numbers in previous posts, here's some rough numbers I calculated:

Say we have a 3000kg payload mass (including power source and engines), 5N thrust, 5000s Isp, we try a solar escape trajectory with Jupiter assist so that we reach Sedna in 10 years.

Assuming a hyperbolic trajectory with Pe around Jupiter orbit, this requires around 40km/s at Pe. Velocity with respect to the sun on arrival at Sedna will be around 36km/s.

For Sedna capture, almost all of this will have to be burned off. That is about a 1 year burn using 3000 kg of propellant.

New Horizons left Jupiter encounter with about 20km/s. If we assume a similar assist, an additional 20km/s delta-v needs to be added. With the now 6000 kg vehicle, that is an additional 1 year burn with 3000kg of propellant.

So we have launch mass = 9 tonnes not including anything we need for the initial Jupiter intercept.

For just a Sedna flyby, we only need 1500 kg of propellant to get to 40km/s leading to a total mass of 4.5 tonnes.

[Streetwind]

9 tons is actually less than I expected. Even a medium lifter like the Falcon 9 can push that much into LEO with mass to spare. ...I'm assuming you're calculating from LEO. Especially since 3 ton dry mass is quite comfortable. The Mars rovers have what, a few hundred kg of science instruments? Curiosity in total weighs just 900kg, including the heavy RTG, drive system and suspension, computers, batteries etc. If the nuclear reactor ends up at 1.5 tons, and an extra 500kg is provisioned for the VASIMR... I don't know how heavy the VF-200 is, but half a ton sounds quite generous. That leaves more than an entire Curiosity's worth of payload just for science and control systems. Very nice. The Mars 2020 rover, a twin to Curiosity, also demonstrates that you can have a compact surface sample collection mechanism as just one of the many various instruments.

According to this dV map, landing on Sedna from a 20km orbit takes about 300 m/s. Not sure where they got that number from, but I do know that Sedna's size and mass hasn't been exactly determined. So let's give it a safety margin and provision a dedicated landing system with around 1000 m/s. The electric propulsion system won't be landing anything anywhere, and storing cryogenics for 10+ years is kind of an issue, so we'll assume hypergolic engines. ESA is currently developing a N2O4/MMH engine specified for 340s Isp, most others are around 320. Provisioning 1 ton of hypergolic propellant for a 3 ton spacecraft yields just over 900m/s with 320s Isp, or barely 960m/s with 340. That sounds reasonable; the entire spacecraft will be able to land, perform experiments/sample collection and take off again. Surely a few kg can be found in the mass budget for landing struts capable of handling a gravity not much in excess of that of Ceres.

Of course that bumps the initial payload from 3 to 4 tons, and the tyranny of the rocket equation makes everything much heavier. And then the successfully orbiting spacecraft is stuck there with the surface samples because we don't have a return stage yet. I simplified and decided to have the entire spacecraft aldn and take off because I'm not sure of the difficulty of performing a fully robotic orbital rendezvous and docking maneuver without human guidance (the communications lag will make interaction with the craft during docking utterly impossible). But potentially this approach might be preferrable, if it means we can leave the spacecraft with its heavy reactor and propulsion/fuel in orbit and just land something maybe the size/weight of a Mars rover. Likely not a rover itself, but rather something that will take off again after a couple weeks of surface science and re-dock with the spacecraft. Which will then need to return to earth in a timely fashion.

How would the numbers look if we assume that the spacecraft that arrives at Sedna weighs, say, 12 tons instead of 3? Whereas the numbers you ran would be an orbit/impactor probe, this variant would be the land and sample return. Assume that it has 10N of thrust instead of 5N, with the same Isp. Would that be feasible, and would a Falcon Heavy or SLS (50-70 tons to LEO) be sufficient to launch that?

Also: What will Sedna's velocity with respect to the sun be at perihelion anyway? I'm not clear on how to calculate that (and I'd like to see your numbers in general, it's interesting).

[Mr Shifty]

Also: What will Sedna's velocity with respect to the sun be at perihelion anyway? I'm not clear on how to calculate that (and I'd like to see your numbers in general, it's interesting).

Sedna's sma (a): 7.7576x10¹⁰ km

Sedna's perihelion ®: 1.1423x10¹⁰ km

Sun's gravitational parameter (GM): 132712440018 km³s^-2

Speed at perihelion from the vis-viva equation:

v=4.64 km/s

However, considering how much larger Sedna's orbit is than that of earth, it would be fairly trivial to find a suitable launch window. Earth simply goes around the sun so fast that Sedna barely moves in comparison. It's like launching towards Jool... from Moho. Regardless where Jool currently is, you just need to wait a couple days until Moho is positioned properly.

You'd almost certainly want to use Jupiter to gravity assist, so the launch window is constrained by Jupiter's orbit, not Earth's.

Edited August 8, 2014 by Mr Shifty

[indroth]

and I'd like to see your numbers in general, it's interesting

Let me try to get all this off the used post-its and miscellaneous scrap that I did it on. Not even sure it's correct, so maybe someone can confirm. But I should probably do some actual work at work today instead of this.

One thing to keep in mind though is that the "tyranny of the rocket equation" is largely in relation to delta-v. Fuel mass is proportional to payload + engine + etc mass for any given delta-v and Isp.

Edited August 8, 2014 by indroth

[Duxwing]

Could gravitational slingshots around the outer planets reduce our propellant requirements by raising our aphelion?

-Duxwing

Edited August 8, 2014 by Duxwing

[Mr Shifty]

Using Arrowstar's Trajectory Optimization Tool for Orbiter, I was able to find a relatively low energy trajectory with a Jupiter assist. (I had to download the ephemeris for Sedna from HORIZONS, which was a much bigger pain than I remember it being.):

Leaves Earth: 24-Mar-2020, TJI from LEO requires 7 km/s (less than half of what New Horizons required)

Jupiter fly-by: 22-Aug-2021 at an altitude of about 140,000 km

Sedna arrival: 11-Sep-2042, relative velocity 17.9 km/s

It's possible to get there faster (e.g. I found a 14 year trip that costs about 10 km/s), but your arrival velocity becomes enormous pretty quickly (>28 km/s for the 14 year trip.)

[Streetwind]

Sedna's sma (a): 7.7576x10¹⁰ km

Sedna's perihelion ®: 1.1423x10¹⁰ km

Sun's gravitational parameter (GM): 132712440018 km³s^-2

Speed at perihelion from the vis-viva equation:

http://upload.wikimedia.org/math/9/9/1/99141ee42424be2c2c2f9c3491ae67d5.png

v=4.64 km/s

Cool, many thanks!

Could gravitational slingshots around the outer planets reduce reduce our propellant requirements by raising our aphelion?

Oh, it definitely can. Thing is though, Sedna is crazy far away. Twice as far as Pluto at bare minimum. At that point, travel time becomes a significant factor, because you need an onboard fission reactor to drive the high powered electric propulsion necessary to take you there. And you cannot refuel that reactor in flight. You must complete the mission before the energy output drops too far from fuel poisoning by fission products. How much time a modern reactor like the SAFE-400 affords us, we don't know. But asking it to go 10-20 years one-way, and then possibly even come back, that's a very tall order.

Any gravity assist you do means you're spending time not flying towards your destination. And if you're required to loop around the Sun, that can take a huge amount of time. Look at Rosetta, how it slingshotted itself into a trajectory similar to that of its target over 10 years without spending much in the way of fuel. A prime example of this strategy, and a prime example of exactly what will not work for Sedna. Not only is there no planetary body available to kick us into a similar orbit - even Neptune is closer to the Sun than it is to Sedna's perihelion - but Sedna has an orbital period of 11,400 years. Even an orbit a fraction of this size would last well beyond anything the spacecraft could support.

This mission will need a trajectory more akin to that of a cannonball shot at Sedna, not a graceful orbital ballet like Rosetta performed. Fly in a line as straight as possible, burning for years without pausing, then flipping over near the end and burning for another half eternity to slow down in time. On a trajectory like this, you can pick yourself one single target and slingshot around that. That's why Mr. Shifty pointed out that it's Jupiter's orbit that will determine the launch window. As the second heaviest object in the solar system by far, it really is the only sensible choice. Maybe, by sheer luck, Uranus or Neptune may line up on the way out to give another boost; but that's just a bonus, and it won't be nearly as helpful as a full-on slingshot that loops you around the planet.

Using Arrowstar's Trajectory Optimization Tool for Orbiter, I was able to find a relatively low energy trajectory with a Jupiter assist. (I had to download the ephemeris for Sedna from HORIZONS, which was a much bigger pain than I remember it being.):

Leaves Earth: 24-Mar-2020, TJI from LEO requires 7 km/s (less than half of what New Horizons required)

Jupiter fly-by: 22-Aug-2021 at an altitude of about 140,000 km

Sedna arrival: 11-Sep-2042, relative velocity 17.9 km/s

It's possible to get there faster (e.g. I found a 14 year trip that costs about 10 km/s), but your arrival velocity becomes enormous pretty quickly (>28 km/s for the 14 year trip.)

Pretty neat, but 2020 looks rather soon. We probably couldn't build a spacecraft by then even if we started now. Is there a later launch window? Perihelion is in 2076, so there's a few decades of buffer still.

Also, 22 years... For reasons outlined above, I'd rather waste dV than spend time coasting. Unless, of course, science suddenly gives us a compact, lightweight reactor that can live that long.

EDIT: Jupiter's orbital period is 11.86 years. So maybe 2031/32 or 2043/44 or 2055/56 could be candidates.

Edited August 8, 2014 by Streetwind

[Duxwing]

Street wind, you seemingly assume the reactor must produce full power whether the engine is firing or not: do you, and why?

If it need not produce power for twenty years, then could the reactor last longer by producing less or no power when the engine is not firing and full power only when the engine is?

-Duxwing

[indroth]

So I just tried replicating my previous calculations and got a launch mass of 97 million kgs. Hooray for beer!

[Streetwind]

Street wind, you seemingly assume the reactor must produce full power whether the engine is firing or not: do you, and why?

If it need not produce power for twenty years, then could the reactor last longer by producing less or no power when the engine is not firing and full power only when the engine is?

I don't know enough about reactors to comment on that. I only know that many nuclear power plants need to be refueled on a yearly basis.

So I just tried replicating my previous calculations and got a launch mass of 97 million kgs. Hooray for beer!

Bottoms up!

[Mr Shifty]

Pretty neat, but 2020 looks rather soon. We probably couldn't build a spacecraft by then even if we started now. Is there a later launch window? Perihelion is in 2076, so there's a few decades of buffer still.

Also, 22 years... For reasons outlined above, I'd rather waste dV than spend time coasting. Unless, of course, science suddenly gives us a compact, lightweight reactor that can live that long.

EDIT: Jupiter's orbital period is 11.86 years. So maybe 2031/32 or 2043/44 or 2055/56 could be candidates.

Yeah, the fact that we're not actively looking to visit these far-flung bodies already is kind of sad. Eris will cross the ecliptic in about 2075 (and not again for 250 years), which means that you could do a fly-by for the next few decades and spend relatively little on an inclination change. (Eris's orbit is inclined 43° to the ecliptic.) If we launched in 2016, we could do a Jupiter->Saturn->Neptune->Eris [thread=85185]trajectory[/thread] that would get there in 2049. It's a really long journey, but probably accomplishable if we'd already been working on it, and what an opportunity for more planetary science on the way.

Arrowstar's optimization tool only contains major planet ephemerides out to 2050. I could calculate later trajectories, but I'd have to download different emphemerides. I could even put an upper limit constraint on the transit time if you want.

[indroth]

Jupiter fly-by: 22-Aug-2021 at an altitude of about 140,000 km

Anything less than 10 Jupiter radii has to cope with high levels of radiation. Radiation shielding may be less mass than the fuel and power required for a boost with a more distant assist though.

Yeah, the fact that we're not actively looking to visit these far-flung bodies already is kind of sad.

...

If we launched in 2016, we could do a Jupiter->Saturn->Neptune->Eris [thread=85185]trajectory[/thread] that would get there in 2049.

Just having a Neptune flyby would be amazing considering there isn't even a plan for that.