How long would it take to drive to the sun?

I'm also not a real rocket scientist, but have played one on Usenet. In my youth I did play with basic orbital equations of the planets and simple satellites, but haven't been anywhere near the multi-body and satellite guidance stuff that Bob and his colleagues use.

The first 24,000 mph is not quite enough to escape Earth's gravity well. You'd need slightly more to climb out. But once out, you are still traveling around the sun at 67,000 mph, just no longer bound to Earth.

Then, after applying a second 24,000 mph burst backwards, your speed is now too slow to stay in Earth's near circular orbit, and you start falling in. Your new orbit is an ellipse, with its aphelion right where you left Earth. But while perihelion will be much closer to the sun, it will still be very high, maybe still higher than Venus (sorry, I haven't reviewed the equations this century), certainly higher than Mercury.

To drop directly into the sun, you need to dump that entire 67,000 mph solar orbit speed, or at least the entire portion moving at a right angle to the sun. But you can get by with dumping slightly less (without the equations handy, I'll give a swag of 60,000 mph) and dropping the orbit to a tight ellipse with perihelion just skimming the far side of the sun. But this 60,000 mph speed change is far far beyond the capability of existing launchers, and it still doesn't include the 24,000 mph initially needed to escape Earth.

The basic orbital equations use energy, not speed, so don't just linearly add the 24,000 and 60,000 mph together to get 84,000 total mph change. 65,000 is enough if done right. But because of the exponential function of fuel mass needed to change speed, this is still a lot more expensive than even 60,000 mph.

In contrast to going to the sun, escaping the solar system requires considerably less speed change -- 67,000 * (squareroot(2)-1) = 28,000 mph in the forward direction. After escaping Earth. Figure 37,000 mph from the ground.

PS. If you want to try some basic math to see how much fuel is needed for a given speed change, see Tsiolkovsky rocket equation. You will need a rocket exhaust velocity. The Space Shuttle main engines were among the best at a hair short of 10,000 mph.

 

Ahha. Yes, I was wrong.

First, thanks to both of you for excellent, clear explanations. This was incredibly helpful.

Second, fuzzy1, I think you noticed something that Bob didn't, possibly because Bob knows so much about the subject that it didn't occur to him that anyone could be as stunningly stupid as I was here. I had of course forgotten that the reason escape velocity is escape velocity is that it's what's required to overcome gravity and be doing very slightly more than 0mph by the time I reach the threshhold. I think your in-depth layman's knowledge meant you could know the answer while not missing my immense silliness.

You've both been really helpful here. Thank you very much.

Who'd have thought that a thread about driving a Prius to the sun at 65mph would have led to something so clear and interesting?

 

...I am just going to procrastinate and wait until the Sun turns into Red Giant and comes closer to Earth.

I am thinking I can get a Gen4 Prius by then, too...

 

So instead of pulse and glide, it's fart and wait?

 

Noooooo...... That's for flights to Mars!

Comet brushes Mars today; Once in a million year event. | Page 2 | PriusChat
....and from that post onwards.

 

You were neither stunningly stupid nor immensely silly. Even though what I wrote fell far short of real rocket science (as does my own knowledge), it still involves more orbital mechanics than I received in ordinary high school and primary college physics. While it can readily be derived from the high school stuff, the great majority of students have not been led far enough down that path to get the 'aha!' moments.

 

That's very kind of you. But I'm not used to making that sort of mistake, so I do feel somewhat foolish.

Thanks again for the explanation, though. It really was extremely clear: you did a great job.

 

When you get into orbit search for 2 black holes lining up with each other and head into the "worm hole". You be at the sun in no time, or, oops, out of the universe!

DBCassidy

 

The wiki on interplanetary transportation network is worth a look. It is slow but it gets you there in a fuel-efficient manner. Which I guess is how this conversation began.

Surprisingly enough, Bob Wilson has not yet posted the horsepower and fuel flow required to drive Prius vertically at 65 mph against the Earth's gravity. Neglecting the absence of tire friction of course. Or of a vertical road.

 

Trick question: the Prius does not have enough power to go vertically at 65 mph. We'll have wait for FCV (Fusion Cell Vehicle):

(Always wondered what one should do with a Miller.)

Bob Wilson

 

... at the surface. The first part of the trip will have a slower climb rate, but could speed up as it climbs out of earth's gravity well.

 

Hummm, I've done multiple benchmarks at maximum acceleration and not seen evidence of a 1G acceleration but that could have been traction control limiting. But if we can use a grade or slope for the lower altitudes, it could work. Of course going vertical, we'd have to use super-grip, tires, or a tube-road:

Source: Michael Schumacher Drives an SLS AMG Upside Down in a Tunnel

Bob Wilson

 

A barrel roll without wings!

Since the Prius won't be doing that, maybe it will have to be modified to cog-drive rails. Or look to the climbing traction systems considered for the future space elevator.

 

The sun is moving at nearly 800,000mph. so the key is to wait until the earth is in the direct path of the sun, and then launch towards the sun. that way you are moving towards the sun @ 65mph, but the sun is now moving towards you at 800,000. think about standing at the caboose end of a train thats moving forward at 60, and you run towards the engine @ 15mph, you net speed over ground is now 75... no need to "lead your target" then either...

so, in thoery if you could just stay in the same place after leaving the earths gravity. the sun would get to you in 116 hours...

93,000,000/800,000

 

A little faster once you get deeper in its gravity well.

 

Hang on....

The Prius i-tech (the top of the range one here, like a Prius 5 in America, I think) comes with solar panels to run the air con.

If we rewire the solar panels to run the electric motor, we'll be able to get more and more power out of the panels as we get closer to the sun, and we'll eventually be able to drive extremely fast.