Spacecraft orientation and navigation

[tblaxland]

Don't the spacecraft also have a rudimentary internal navigation as a backup? Something along the lines of taking in to account all engine burn times, amounts of thrust applied, and in witch vector, and for how long. Also taking in to account star-tracking data, and anything else the spacecraft can measure. And determining from that what the orbit should be.

Yes, they have onboard nav/state vector propagation systems. I don't think onboard burn targeting is generally provided though (eg, for MCCs).

That's very cool, I didn't know they could do that.

Ain't it just? Cool what they could do with so little processing power, and cool that they could use optical celestial navigation just like in the golden ages of maritime exploration. Ever since I started exploring optical navigation in Orbiter, I have been itching to get my hands on one of these from the Australian National Maritime Museum (of which I am a member):

 

[SiberianTiger]

Ah, cool. Collect data, transmit to ground, wait for computer to spit out an orbit plot. I had always kind of wondered if they were really just executing a well-planned dart throw.

Which was the case with the early lunar probes. And even more so, with Japanese Lambda rocket (artificially impaired of guidance).

 

[Ark]

The whole sextant thing is very cool. Makes sense when you think about it, across the vastness of planetary space, the stars around us don't appear to move a millimeter.

That'll probably be a major part of navigation on a Mars mission, the time delay en route would necessitate navigating accurately from the ship itself.

 

[tblaxland]

That'll probably be a major part of navigation on a Mars mission, the time delay en route would necessitate navigating accurately from the ship itself.

The time delay is not really an issue since it is predictable and measurable and you can take account of it in the guidance computations. When you have people onboard though, you do want to make sure they can navigate in the event of loss of comm.

 

[Andy44]

That'll probably be a major part of navigation on a Mars mission, the time delay en route would necessitate navigating accurately from the ship itself.

Not really. The time delay from Mars is measured in minutes, which is very short, while a good orbit propagation will be valid for days on end, and propulsive maneuvers will be planned many hours in advance, perhaps even days.

But it is important as a redundant back-up procedure in case of loss of comm, and also to give the crew the confidence that they can steer their own ship using their own skills like a real pilot if it comes down to it.

 

[Turbinator]

I have been itching to get my hands on one of these from the Australian National Maritime Museum (of which I am a member):

http://www.stanleylondon.com/sextcaptain.htm
$220

 

[Urwumpe]

Don't the spacecraft also have a rudimentary internal navigation as a backup?

Most modern spacecraft have, but Apollo didn't have a full INS. The IMU of Apollo was only activated for burns or during reentry, but most of the time it was shutdown for saving power. The many star sightings are not just for improving the navigation solution but also for aligning the IMU optimally for the next maneuver, the coordinate system of the IMU had always been relative to the next maneuver.

This was one big limitation compared to Gemini and Shuttle - Gemini and Shuttle both had(have) permanent INS, but both had also been designed AFTER Apollo.

 

[Turbinator]

I am trying to find this book in a library near me, no luck so far. If you can get your hands on one it is an excellent read.

How Spacecraft Fly: Spaceflight Without Formulae By Graham Swinerd

The book will open with a concise introductory chapter, chronicling the 'space age' up to the present, and a brief 'forward look' into near–future developments. Chapter 2 provides the historical context upon which the current developments in spaceflight have been built. Orbital motion will be introduced in Chapter 3, and how to get there using launch vehicles is addressed in Chapter 4. Chapters 5 and 6 look at how spacecraft are designed, and Chapter 7 addresses the additional design constraints imposed if the spacecraft has a human crew on board. Chapter 8 gives examples of current and proposed spacecraft missions, both Earth orbiting and interplanetary. Chapter 9 will look at near future manned flight developments – for example, a mission to Mars and/or space tourism. The book closes with a concluding chapter, which reflects on prospects for the future of robotic and manned space exploration.

Here is a Google Books preview:
http://books.google.ca/books?id=FU0...resnum=1&ved=0CAkQ6AEwAA#v=onepage&q=&f=false

 

[JamesG]

I guess "Space Flight for Dummies" was already taken?

It is possible to astronavigate with nothing but a sextant, clock, astronomical charts, notepad, and the ability to do college level calculus.

I imagine that someday there will be a sport of "space sailing" where vessels are flown around the solar system with only solar sails for propulsion and the pilot's wits and knowledge for navigation.

 

[Urwumpe]

I imagine that someday there will be a sport of "space sailing" where vessels are flown around the solar system with only solar sails for propulsion and the pilot's wits and knowledge for navigation.

You may laugh but I actually thought about making such minimal sport ships as Orbiter add-on, only with such kinds of tools...

 

[JamesG]

Same here. You would have to create an entirely new navigation interface. Instead of MDFs you create a sextant "sight picture" to take readings, and a chart of astronomical figures. I guess you could spoil people with a digital calculator and a "cheat sheet" of formulas.

It would be a great way of teaching orbital dynamics even more directly than Orbiter already does.

 

[Andy44]

I believe there is a sextant MFD around here somewhere. A.C. Clarke wrote a short story about a solar regatta race once, was very cool.

 

[Urwumpe]

I believe there is a sextant MFD around here somewhere. A.C. Clarke wrote a short story about a solar regatta race once, was very cool.

Well, sextant alone wouldn't hit it. You would also a lot of other stuff and tables...but you could for example calculate the radius to a planet by the observed size, and hit it into a simple chart plotter... But you could sure do without an electronic guidance computer.

If you use just simple engines (pressure fed) for maneuvers, you could even do without any engine electronics, though that would be likely the least concern for sports.

 

[orb]

I believe there is a sextant MFD around here somewhere.

It's on tblaxland's bitbucket: http://bitbucket.org/tblaxland/sextant-mfd/downloads/

 

[tblaxland]

It's on tblaxland's bitbucket: http://bitbucket.org/tblaxland/sextant-mfd/downloads/

Thanks for posting that. I should get around to putting that on OH once the new server is up and running. Please note that MFD was specifically designed for the purpose of optical rendezvous. If anyone manages to achieve anything else useful with it, please let me know

 

[Izack]

You may laugh but I actually thought about making such minimal sport ships as Orbiter add-on, only with such kinds of tools...

Want.

That's just the sort of challenge I would love. As it is I spend most of my Orbiter time sailing the Solar System without such tools as IMFD or TransX, and I've been mulling around the idea of building a Planetary/Orbital Analysis Kit for Orbiter that would help you explore without 'cheating' by reading Orbiter's physics engine.
If someone with much more skill/know-how than I were to do that I would be very grateful.

EDIT: Holey moley I just realised how old this thread is. :embarrassed: