48 Hours Of Thrust Roundtrip Around The Solar System And Back

[Spacescifi]

48 Hours Of Thrust Round Trip

The Scenario: You have a propellantless scifi spaceship that can thrust up to 5g acceleration or less with 2000 ton payload. Max thrust is even higher if you reduce payload, but unlike normal rockers it WON'T your fixed ISP if you lower thrust. It runs off highly engineered fuel that can only be made or found back on Earth for now. Unless you drop 1 ton fuel packs elsewhere in the solar system. You will not be allowed to use any of the 1 ton fuel packs you seed throughout the system to fuel your vessel. Since that will be for future explorers. You are running off one fuel pack.

Don't worry about how or why it flies. All I want to know is how far it can go roundtrip in the solar system and back to Earth.

Assumptions: It would be foolish to waste thrust time, so I presume some coasting is in order. Even so, with thrust levels/times like these we can point and scoot wherever we want in the solar system.

Questions:

1. What do planetary travel times look like with this drive?

2. Conservative travel times where you are trying to save on thrust time/fuel?

3. ASAP travel times where you don't care about wasting fuel and only want to reach a planet ASAP before the return trip to Earth.

4: What is your 2000 ton payload since it won't be propellant? What is your objective? Seeding fuel packs for future explorers? Dropping off colony equipment for other worlds? Research probes?

5. Where would you drop fuel packs? In orbit? Or on a moon or planet in a shallow grave covered with regolith and a beacon broadcasting it's location?

Edited May 8, 2021 by Spacescifi

[cubinator]

Let's say you want to deliver some building supplies to Neptune. They are metal beams, panels, etc that can take the acceleration. They are the stage for a surprise birthday party for the Neptunian President, Mr. Joel Poseidon, and need to be delivered ASAP so that the birthday bash can begin on time. 5 gees for that amount of time is so high that we won't have to bother with orbital mechanics for the most part. Our path will be pretty much a straight line there and back. We need to accelerate forward for half the time, and then backward for the second half in order to not destroy a small moon by kinetic energy alone upon arrival. 

velocity: v= 5*9.81*t

position: p=∫v dt = 5/2 * 9.81 * t²

distance: d = 4.3e12 m

Integrating the velocity over half the time...

p = 2.15e12 m

2.15e12 = 5/2 * g * (t/2)² - 0

t = 592168 seconds. So you can make it to Neptune by flying for one week on 5 gees.

Since the g load is just a multiplier, you can change it to see what the time is for other accelerations. In a more comfortable 1 g, it would take 34 days to reach Neptune. Not quite enough to deliver a warm pizza, even to Mars (10 hours, even at closest approach).

Oops, I didn't read about the 48 hour limitation. That would change things up a little bit and make the integrals a little more curvy. I don't have time to do those calculations right now.

Edited May 8, 2021 by cubinator

[kerbiloid]

48 minutes ago, Spacescifi said:

1. What do planetary travel times look like with this drive?

5 g? Like rodeo.

When the horse has fallen above.

[Spacescifi]

38 minutes ago, cubinator said:

Let's say you want to deliver some building supplies to Neptune. They are metal beams, panels, etc that can take the acceleration. They are the stage for a surprise birthday party for the Neptunian President, Mr. Joel Poseidon, and need to be delivered ASAP so that the birthday bash can begin on time. 5 gees for that amount of time is so high that we won't have to bother with orbital mechanics for the most part. Our path will be pretty much a straight line there and back. We need to accelerate forward for half the time, and then backward for the second half in order to not destroy a small moon by kinetic energy alone upon arrival. 

velocity: v= 5*9.81*t

position: p=∫v dt = 5/2 * 9.81 * t²

distance: d = 4.3e12 m

Integrating the velocity over half the time...

p = 2.15e12 m

2.15e12 = 5/2 * g * (t/2)² - 0

t = 592168 seconds. So you can make it to Neptune by flying for one week on 5 gees.

Since the g load is just a multiplier, you can change it to see what the time is for other accelerations. In a more comfortable 1 g, it would take 34 days to reach Neptune. Not quite enough to deliver a warm pizza, even to Mars (10 hours, even at closest approach).

Oops, I didn't read about the 48 hour limitation. That would change things up a little bit and make the integrals a little more curvy. I don't have time to do those calculations right now.

 

Constant acceleration high thrust the whole way is too OP for me. Also seems too unrealistic or at least too easy.

Edited May 8, 2021 by Spacescifi

[cubinator]

3 hours ago, Spacescifi said:

Constant acceleration high thrust the whole way is too OP for me. Also seems too unrealistic or at least too easy.

6 days at 5 gees is not that much more than 2 days at 5 gees, though. You're two steps from constant thrust anyway. Does the engine get hot and need to cool down after two days? Or is there only enough boom juice to run it that long in total? With only three times the given limit, Neptune in a week becomes feasible.

The farthest you could go with constant thrust for 48 hours is 366 million km. That'll get you to Mars at almost any phase, and in any case you'd only have to coast for about 60 million km. Venus and Mercury are constant thrust trips, and if you timed it right you could make it to Ceres and probably anything in the inner Main Belt. So only the outer solar system is really going to involve any sort of coasting.

[Spacescifi]

18 minutes ago, cubinator said:

6 days at 5 gees is not that much more than 2 days at 5 gees, though. You're two steps from constant thrust anyway. Does the engine get hot and need to cool down after two days? Or is there only enough boom juice to run it that long in total? With only three times the given limit, Neptune in a week becomes feasible.

The farthest you could go with constant thrust for 48 hours is 366 million km. That'll get you to Mars at almost any phase, and in any case you'd only have to coast for about 60 million km. Venus and Mercury are constant thrust trips, and if you timed it right you could make it to Ceres and probably anything in the inner Main Belt. So only the outer solar system is really going to involve any sort of coasting.

Not enough boom juice...vessel could carry a lot more for personal use but safety regulations stipulate dropping them for future explorer vessels to utilize.

Edited May 8, 2021 by Spacescifi

[YNM]

5 hours ago, Spacescifi said:

Assumptions: It would be foolish to waste thrust time, so I presume some coasting is in order.

Correction : It would be a waste not to accelerate any part of the precious 48 hour window. Lunar free-return trajectory is already a 6 days round trip.

[Spacescifi]

5 minutes ago, YNM said:

Correction : It would be a waste not to accelerate any part of the precious 48 hour window. Lunar free-return trajectory is already a 6 days round trip.

 

It's not time window.

It only starts ticking when you use it.

Coasting saves it for later use.

[YNM]

5 minutes ago, Spacescifi said:

It only starts ticking when you use it.

So you're saying that you can accelerate at 5 gees for 48 hrs straight ?

That's just plain old dV then...

 

So 49.033 m/s2 multiplied by 172,800 seconds : 8,472,945.6 m/s dV budget, or 0.02826 c (2.826% of the speed of light).

Edited May 8, 2021 by YNM

[Spacescifi]

6 minutes ago, YNM said:

So you're saying that you can accelerate at 5 gees for 48 hrs straight ?

That's just plain old dV then...

 

So 49.033 m/s2 multiplied by 172,800 seconds : 8,472,945.6 m/s dV budget, or 0.02826 c (2.826% of the speed of light).

 

Yes.

[JoeSchmuckatelli]

I remember hearing waaaay back in highschool that the fastest way we have to get anywhere in the solar system is as @cubinator described it: full bore thrust half- way to the destination, flip, full bore decel until you get there.

My understanding of why we 'coast' to Mars & etc. in the solar system today is that we are willing to trade time for resources - given we can't get enough propellant to space to do the above.

...so I'm not understanding what you're asking when you're requiring some coast time and setting a 48 hour limit.

[Spica]

Just to give you an idea of the energy scales required for this task:

Accelerating 2,000 tons up to 8,500 km/s with a rocket requires at minimum 1.11*10^20 Joules, or around 25 Gigatons TNT equivalent. This is with a propellant mass ratio of 4.922, and negligible structural (non payload) mass.

The power required to perform this task is also on the order of 140 kilotons per second.

This task can be performed with Uranium as the energy source, but it will require about 1300 of your 1 ton modules, and that's just for the energy requirement, you'll need even more to account for the propellant you need to do this.

If instead for example DT fusion powers this, the "radius of instant death" for unshielded people is on the order of hundreds of kilometers.

Edited May 9, 2021 by Spica
correction

[cubinator]

44 minutes ago, JoeSchmuckatelli said:

My understanding of why we 'coast' to Mars & etc. in the solar system today is that we are willing to trade time for resources - given we can't get enough propellant to space to do the above.

Yes - it would require a ludicrous amount of propellant to do this type of flight by the options available today. Note that we do have some options (like ion propulsion) that could potentially do constant thrust to places like Mars and Venus, and would be faster than the minimum energy routes, but with very, very low thrust.

44 minutes ago, JoeSchmuckatelli said:

...so I'm not understanding what you're asking when you're requiring some coast time and setting a 48 hour limit.

For science-fiction worldbuilding purposes.

[JoeSchmuckatelli]

1 hour ago, JoeSchmuckatelli said:

'm not understanding what you're asking when you're requiring some coast time and setting a 48 hour limit.

 

11 minutes ago, cubinator said:

For science-fiction worldbuilding purposes.

I get that -- I'm just having a dense moment and can't picture what he's asking.  Is the round-trip tour of the solar system supposed to happen in 48 hours, or are you straight flaming for 48 hours and then coasting for a while followed by another 48 hours of decel, or do you have only enough fuel for a total of 48 hours of burn time and want to see how much of the planets you can get on that amount of thrust?

 

that's what I'm trying to winkle out

.

[Spacescifi]

1 hour ago, JoeSchmuckatelli said:

I remember hearing waaaay back in highschool that the fastest way we have to get anywhere in the solar system is as @cubinator described it: full bore thrust half- way to the destination, flip, full bore decel until you get there.

My understanding of why we 'coast' to Mars & etc. in the solar system today is that we are willing to trade time for resources - given we can't get enough propellant to space to do the above.

...so I'm not understanding what you're asking when you're requiring some coast time and setting a 48 hour limit.

 

Why?

Too overpowered otherwise.

If anything can just high thrust indefinitely you can stick on disposable missiles and NOTHING will stop you but other missiles just like them.

 

As matters are, that can happen still but it is less likely since thrust time is not unlimited.

1 minute ago, JoeSchmuckatelli said:

 

I get that -- I'm just having a dense moment and can't picture what he's asking.  Is the round-trip tour of the solar system supposed to happen in 48 hours, or are you straight flaming for 48 hours and then coasting for a while followed by another 48 hours of decel, or do you have only enough fuel for a total of 48 hours of burn time and want to see how much of the planets you can get on that amount of thrust?

 

that's what I'm trying to winkle out

.

 

I am saying that the fuel pack IS also your propellant and power!

This is a scifi drive, not a typical rocket, which is why refueling off natural resources is not an option.

It actually emits no gas or plasma exhaust.

Just scifi  light rays that are strong carriers of magnetic force.

The nozzles are polarized and are strongly repelled when the repulsive rays fly out, losing magnetice force with distance.

[JoeSchmuckatelli]

@Spacescifi wait - you're just thinking in terms of a weapon?  I did not get that when reading the OP.  I thought you were wanting to get stuff or people to the place(s) safely.

Edited May 9, 2021 by JoeSchmuckatelli

[Spacescifi]

3 minutes ago, JoeSchmuckatelli said:

@Spacescifi wait - you're just thinking in terms of a weapon?  I did not get that when reading the OP.  I thought you were wanting to get stuff or people to the place(s) safely.

 

I was not...but we both know any good transport can double as a weapon....which is why I don't want it TOO good.

 

Just would take one ir a few programmed doomsday robot vessels to reach light hugger speed and collide with Earth with little options for stopping them and not much time either otherwise.

[kerbiloid]

Several days at 5 g is not a good transport.
It's crew's brains in boots.

[cubinator]

6 hours ago, kerbiloid said:

Several days at 5 g is not a good transport.
It's crew's brains in boots.

You'd DEFINITELY limit this to 1 g or so for crew, but I think 5 g would be manageable for many kinds of flat-packed inanimate objects.

[YNM]

11 hours ago, JoeSchmuckatelli said:

or do you have only enough fuel for a total of 48 hours of burn time and want to see how much of the planets you can get on that amount of thrust?

Given OP OK-ed my dV calculation I suppose this is the idea.

14 hours ago, YNM said:

[...] So 49.033 m/s2 multiplied by 172,800 seconds : 8,472,945.6 m/s dV budget, or 0.02826 c (2.826% of the speed of light).

Edited May 9, 2021 by YNM

[Shpaget]

On 5/9/2021 at 12:06 AM, YNM said:

2.826% of the speed of light

Basically, anywhere, everywhere and back. Long way around, if you please.

Multiple times.