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#1 2018-04-28 09:33:01

Oldfart1939
Member
Registered: 2016-11-26
Posts: 1,714

GPS system for Mars?

Since there has been much discussion regarding landing accuracy of the under construction SpaceX BFS/BFR, this is probably the place for ongoing discussion of that specific topic.

The accuracy in landing of the SpaceX Falcon 9 rockets, both at Cape Canaveral A.F. Station and on the 2 drone ships, Of Course I still Love You and Just Read the Instructions, is only made possible through the existing system of Earth GPS satellites, coupled with ground based transponders called the WAAS system, or Wide Area Augmentation System. The drone ships undoubtedly are so equipped with their own onboard transponders.

It appears that there is but one game in town for building these GPS satellites. And that's Lockheed Martin, since both Boeing and Northrup Grumman have declined placing bids in the USAF most recent RFP. The price stated from LockMart for a single GPS satellite is ~ $6 Million, and Mars would probably require a constellation of 10 to 14 such systems. For optimal location accuracy a landing aircraft requires that 3 satellites be in communication with an onboard receiver; that amount of data allows an Earthbound airliner or landing rocket to make an approach but not autoland; the additional ground-based transponders of the WAAS system are what allows most airliners landing at major airports to use the autoland system.

I need to do some research on the mass involved with the GPS satellites, but I'm guessing that a Falcon Heavy could probably launch a package of 3 to 5 of them the Mars orbit insertion. I also don't know what else would be needed. Even a set of 5 GPS satellites would definitely improve the landing accuracy by an order of magnitude over having NONE. Then a follow-up Red Dragon size spacecraft could be landed for use as a radar transponder at or near a desired site for terminal guidance accuracy of BFS.

Last edited by Oldfart1939 (2018-04-28 09:37:03)

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#2 2018-04-28 11:56:42

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 16,141

Re: GPS system for Mars?

The size of the satellites do not need to be huge in size as the only function that they will need to do is transmit where they are above the planet. These can be small about the size of a cube sat which would allow for a one shot setup of all the required quantity of them.

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#3 2018-04-28 12:08:33

Oldfart1939
Member
Registered: 2016-11-26
Posts: 1,714

Re: GPS system for Mars?

SpaceNut-
Not necessarily true. Once placed in orbit, they need to be stabilized without any orbital changes of significance. The military GPS satellite all mass about a Tonne, with onboard fuel for periodic orbit corrections. For a temporary, quick and dirty approach, the cubesat constellation might serve for 1 or 2 transfer windows. If we're going to Mars for a continued stay, then an approach similar to that formulated by the Air Force using the larger and more permanent type--lifetime of ~ 15 years.

Last edited by Oldfart1939 (2018-04-28 12:09:22)

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#4 2018-04-28 14:49:05

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 16,141

Re: GPS system for Mars?

Agreed that its a cheap and dirty but these are typically college built for nearly free so sending many more on each mission would be good business for the colleges and for any manned mission but yes a fuel reservoir does make it so that they can station keep orbit.

So solving the surface beacon much in the same manner means lots of low cost landing will be needed as well.

But after the first few missions to populate the landing areas means we will be doing pin point landing with a great deal of safety.

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#5 2018-04-28 15:19:15

Oldfart1939
Member
Registered: 2016-11-26
Posts: 1,714

Re: GPS system for Mars?

Another important feature will be for on-surface navigation of Rovers. With a good GPS satellite system, travel out of visual and short radio range will be possible and much safer. Since Mars has no effective magnetic field, compasses aren't an option.

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#6 2018-04-28 15:23:38

Oldfart1939
Member
Registered: 2016-11-26
Posts: 1,714

Re: GPS system for Mars?

I'm also afraid that the college built cubesats will not be a viable alternative to larger systems. What will be the source of power? They will need solar panels to remain viable, along with a means of tracking the Sun. My thought is they will be built under contract for SpaceX by--maybe--Lockheed Martin? They could be semi-mass produced as cheaper Earth GPS systems.

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#7 2018-04-28 16:01:14

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 16,141

Re: GPS system for Mars?

http://spacenews.com/congressional-audi … rial-base/

https://www.globalcomsatphone.com/hughe … costs.html

https://defensesystems.com/articles/201 … ccess.aspx

It is estimated that a single satellite launch can range in cost from a low of about $50 million to a high of about $400 million. The next-generation GPS constellation now in development. A GPS satellite cost $43 million to build and $55 million to launch in early 1990s. GPS III satellites will cost an estimated $500 million each and $300 million to launch.
http://spacenews.com/spacexs-low-cost-w … orce-says/

The Air Force announced the award for the February 2019 GPS 3 launch March 14. Leon declined to discuss how SpaceX’s $96.5 million bid compared to any other offers the Air Force received.

GPS is a constellation of 24 satellites that now can tell everyone where he or she is in the world (the initial constellation cost $12 billion to put into orbit). The operating cost works out to just over $2 million a day.

https://www.scientificamerican.com/arti … -research/

Conventional weather satellites are individually constructed and can cost as much as $3 billion to $5 billion to develop and launch.

https://makezine.com/2014/04/11/your-ow … re-you-go/

https://www.gps.gov/applications/space/

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#8 2018-04-28 16:28:04

Oldfart1939
Member
Registered: 2016-11-26
Posts: 1,714

Re: GPS system for Mars?

SpaceNut-
I believe that some of your articles listed above serve to illustrate why the "quick and dirty" method of using cubesats is not the way to do things. Using Falcon Heavy launches incorporating Block 5 boosters, the constellation of Mars GPS satellites could be made functional less expensively than those for the Air Force.

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#9 2018-04-28 17:16:05

kbd512
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Registered: 2015-01-02
Posts: 2,957

Re: GPS system for Mars?

I don't think we want our precision navigation system to be as cheap as we can possibly make it.  Lives are dependent upon that system functioning properly 100% of the time.  Let's just use what we already know works and implement ion propulsion for both delivery to Mars and station keeping at Mars.

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#10 2018-04-28 17:45:45

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 16,141

Re: GPS system for Mars?

How Many Man-Made Satellites Are Currently Orbiting Earth?

GPS satellites are at 12,400 miles, high enough to be accessible to large swaths of the Earth.

https://www.gps.gov/systems/gps/space/

The satellites in the GPS constellation are arranged into six equally-spaced orbital planes surrounding the Earth. Each plane contains four "slots" occupied by baseline satellites. This 24-slot arrangement ensures users can view at least four satellites from virtually any point on the planet.

https://www.space.com/19794-navstar.html

aHR0cDovL3d3dy5zcGFjZS5jb20vaW1hZ2VzL2kvMDAwLzAyNi8yNDQvb3JpZ2luYWwvRmlndXJlXzFfNjUwLmpwZw==

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#11 2018-04-28 17:55:49

louis
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From: UK
Registered: 2008-03-24
Posts: 4,896

Re: GPS system for Mars?

I posted this earlier on another thread:

https://www.osapublishing.org/ao/abstra … 56-10-2597

It appears it is possible to use lasers for communication during the plasma phase.

I suspect Space X will be working on this.  Certainly they haven't mentioned any plans for a Mars GPS system as part of Mission One. I can only imagine it would add huge expense - so best avoided. But a simple laser communication system? That could be the perfect solution.


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#12 2018-04-28 19:27:10

kbd512
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Registered: 2015-01-02
Posts: 2,957

Re: GPS system for Mars?

Louis,

I don't care about whether or not lasers or microwaves are used for communications and navigation.  The point is that the mission requires satellites overhead that can relay precise location information to the navigation computers aboard the BFS so that any necessary course corrections can be made at the appropriate time.  Each BFS can use its own laser communications system to relay the position of other BFS units on the ground to avoid having any collisions.  That said, there's nothing inexpensive about laser communications systems.

Incidentally, spacecraft laser communications is another technology pioneered by NASA, not SpaceX.  LADEE, LCRD, and LEMNOS are all NASA laser communication systems tests.  LEMNOS is supposed to fly aboard Orion when it makes its first flight around the moon.  It's true that the system requires smaller satellites than RF based technologies because less power is required and the laser equipment involved is more compact, but it still uses satellites to relay signals because it's a line-of-sight system.

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#13 2018-04-28 20:39:28

louis
Member
From: UK
Registered: 2008-03-24
Posts: 4,896

Re: GPS system for Mars?

Laser beams would deliver the same precise info as radio communication! smile No satellites would be required as there would be Cargo BFSs on the surface with the required laser guidance equipment.

kbd512 wrote:

Louis,

I don't care about whether or not lasers or microwaves are used for communications and navigation.  The point is that the mission requires satellites overhead that can relay precise location information to the navigation computers aboard the BFS so that any necessary course corrections can be made at the appropriate time.  Each BFS can use its own laser communications system to relay the position of other BFS units on the ground to avoid having any collisions.  That said, there's nothing inexpensive about laser communications systems.

Incidentally, spacecraft laser communications is another technology pioneered by NASA, not SpaceX.  LADEE, LCRD, and LEMNOS are all NASA laser communication systems tests.  LEMNOS is supposed to fly aboard Orion when it makes its first flight around the moon.  It's true that the system requires smaller satellites than RF based technologies because less power is required and the laser equipment involved is more compact, but it still uses satellites to relay signals because it's a line-of-sight system.


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#14 2018-04-28 22:07:42

Oldfart1939
Member
Registered: 2016-11-26
Posts: 1,714

Re: GPS system for Mars?

Louis-
Sure; the wreckage of the first BFR cargo ship will send by laser, the necessary approach information required for the BFS. You fail completely to understand the overall complexity of the guidance required for all stages of planetary approach, atmospheric entry and terminal guidance to touchdown.
The simplistic assumption that your system will be infallible is preposterous. I have a Private Pilot Certificate, all the necessary flight hours for a commercial certificate, and about 30 hours of training towards an instrument rating; everything I've learned about GPS navigation is contrary to your certitude that "all will be well because St. Elon say it will be so." A safe landing on Mars is probably the most dangerous aspect of the entire undertaking in a mission to the Red Planet. There is NO ROOM FOR FAILURE.
If you doubt that others care about this--check GW's comments on the word "assume."

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#15 2018-04-29 06:59:24

louis
Member
From: UK
Registered: 2008-03-24
Posts: 4,896

Re: GPS system for Mars?

Well let's suppose you are right and the first BFR cargo ships (two are planned) both crash land...then there will be no human mission two years later. Simple as that.

But if they do land successfully they can potentially communicate via laser with the human BFS, as well as by transponder.  It would be interesting to know if Space X are looking into this possibility.

I don't have a religious faith in "St Elon", I have a high degree of confidence which I think is justified by events to date.

Previous efforts to reach Mars have been in v. small landing craft - all robotic. At least accept this will be a very different sort of mission with far better comms with Earth, and will also benefit from the huge amount of satellite surveying that has taken place over the last few years (one of the few really good investments by NASA and ESA).

I doubt that Musk is going to land other than in the middle of a large plain to give plenty of room for being off target for the initial cargo ships.  And I think that once you have those cargo BFSs there, there  are ways to ensure accurate landing by the human BFS that follows.

Oldfart1939 wrote:

Louis-
Sure; the wreckage of the first BFR cargo ship will send by laser, the necessary approach information required for the BFS. You fail completely to understand the overall complexity of the guidance required for all stages of planetary approach, atmospheric entry and terminal guidance to touchdown.
The simplistic assumption that your system will be infallible is preposterous. I have a Private Pilot Certificate, all the necessary flight hours for a commercial certificate, and about 30 hours of training towards an instrument rating; everything I've learned about GPS navigation is contrary to your certitude that "all will be well because St. Elon say it will be so." A safe landing on Mars is probably the most dangerous aspect of the entire undertaking in a mission to the Red Planet. There is NO ROOM FOR FAILURE.
If you doubt that others care about this--check GW's comments on the word "assume."


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#16 2018-04-29 07:29:05

louis
Member
From: UK
Registered: 2008-03-24
Posts: 4,896

Re: GPS system for Mars?

It appears the development of laser guidance landing (with Mars in mind) is already well advanced:

https://www.nasa.gov/feature/langley/la … g-missions

So I think my hunch there was correct.


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#17 2018-04-29 08:10:56

GW Johnson
Member
From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 3,643
Website

Re: GPS system for Mars?

Louis:

The Russian paper and the NASA article about laser technology for guidance or communication that you cited are examples of a science feasibility demonstration,  and not even the same application at that. 

It's usually about 20 years (sometimes a lot longer) from that science feasibility point to a feasible technology to use,  if it leads to any at all (many don't).  You need to understand the difference between science on the one hand and real engineering technology on the other.  Apparently,  you don't.  You're not alone,  I see that often in some responses on these forums.

Whether it's radio or laser I don't care,  but some sort of positioning system is needed at Mars for precise trajectory control leading to the beginning of entry aerobraking.  We have such here on Earth,  and it is a great part of how Spacex is landing first stages.  There is nothing yet at Mars suitable for managing direct-entry trajectories.  That lack makes the landing error fall at least in the 10's of km range.

The Russian paper cites an experiment indicating it may be possible to communicate through the plasma sheath during entry with lasers.  Maybe. Maybe not.  That result has yet to be replicated,  much less turned into a working technology.  Don't hold your breath waiting for it. 

Meanwhile there is inertial navigation control,  which has worked during reentry since the very first capsules reached orbit,  over half a century ago.  Why would we ever not continue using it in favor of some speculation about the future of lasers?  That makes no common sense at all. It's just 3-axis gyros and integrating accelerometers.  Predates computers actually,  but it's even better with computers now.

Once you come out of hypersonics and radio works again,  the simple radar beacon on the landing site,  with a homing system on board the vehicle,  will work.  This has been proven in radar missile guidance since the 1950's,  and has gotten rather good with the advent of sophisticated longer-range autonomous seekers in things like AMRAAM and its Russian counterpart AA-12. That gets you within 1's to 10's of meters of your aimpoint,  and that's good enough. Why would we not use that?  Makes no common sense not to.

So the only shortfall here for precision landing on Mars is a swarm of positioning satellites in orbit about Mars of adequate capability to manage direct-entry trajectories.  We already know how to build them.  We already have heavy lift rockets already that can send them to Mars,  and will soon have an even better one (Falcon-Heavy).  The only thing lacking is somebody bellying up to the bar to pay for doing this (and I bet Musk is already talking to NASA about doing it,  behind the scenes).  You solve that lack by who you vote for,  and who they nominate to lead the agencies.

GW

Last edited by GW Johnson (2018-04-29 08:31:50)


GW Johnson
McGregor,  Texas

"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"

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#18 2018-04-29 09:09:13

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 16,141

Re: GPS system for Mars?

I have actually done a Mem's design for being able to do the XYZ accelerometer alignment. It allowed for better acuracy of hitting a target at distance from being hand held. The design replaced a mechanical version.

The laser communications will be simular to the TV remote system and for IR wireless head phones listening systems. The laser beam is not culminated but is spread out and the reciever does the opposite in pulling the light back to the sensor via lenses. Laser power must be enough to compensate for distance to the reciever as the distance increases and it light level attenuates to the recieved signal..

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#19 2018-04-29 09:31:25

elderflower
Member
Registered: 2016-06-19
Posts: 1,115

Re: GPS system for Mars?

The satellite constellation will have a second function. In the absence of a reflective ionosphere, not much more than line of sight communication will be available without satellite relays. They would also allow communication with Earth when it is not in the Martian sky. This could be done by a bunch of satellites apart from the positioning ones, but why would you do that?

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#20 2018-04-29 10:02:48

GW Johnson
Member
From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 3,643
Website

Re: GPS system for Mars?

I'm no electronics guy,  I was an aero/thermal/mechanical type.  But in my old defense career,  I had to know about seekers,  how they worked,  and how good they were. 

Had to know a little about all sorts of missile guidance.  Was required,  whether working in missile development,  or in the countermeasure business that caused them to miss.  And I did both.

But what I did the most was propulsion.  Mostly rocket and ramjet,  but I know quite a bit about turbine,  pulse detonation,  air turborocket,  and the rest. 

GW


GW Johnson
McGregor,  Texas

"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"

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#21 2018-04-29 16:53:59

louis
Member
From: UK
Registered: 2008-03-24
Posts: 4,896

Re: GPS system for Mars?

It wasn't 20 years during WW1 or WW2 or the era of Cold War space competition!  The armoured tank was developed in about 2 years. Jet aircraft were developed in about 3 years flat. A nuclear bomb was produced in 4 years from a standing start. The lunar landing project was put together in about 5 years.

The idea we couldn't master the laser landing technology in under five years I find laughable. It's just a question of willpower, good management and money.

GW Johnson wrote:

Louis:

The Russian paper and the NASA article about laser technology for guidance or communication that you cited are examples of a science feasibility demonstration,  and not even the same application at that. 

It's usually about 20 years (sometimes a lot longer) from that science feasibility point to a feasible technology to use,  if it leads to any at all (many don't).  You need to understand the difference between science on the one hand and real engineering technology on the other.  Apparently,  you don't.  You're not alone,  I see that often in some responses on these forums.

Whether it's radio or laser I don't care,  but some sort of positioning system is needed at Mars for precise trajectory control leading to the beginning of entry aerobraking.  We have such here on Earth,  and it is a great part of how Spacex is landing first stages.  There is nothing yet at Mars suitable for managing direct-entry trajectories.  That lack makes the landing error fall at least in the 10's of km range.

The Russian paper cites an experiment indicating it may be possible to communicate through the plasma sheath during entry with lasers.  Maybe. Maybe not.  That result has yet to be replicated,  much less turned into a working technology.  Don't hold your breath waiting for it. 

Meanwhile there is inertial navigation control,  which has worked during reentry since the very first capsules reached orbit,  over half a century ago.  Why would we ever not continue using it in favor of some speculation about the future of lasers?  That makes no common sense at all. It's just 3-axis gyros and integrating accelerometers.  Predates computers actually,  but it's even better with computers now.

Once you come out of hypersonics and radio works again,  the simple radar beacon on the landing site,  with a homing system on board the vehicle,  will work.  This has been proven in radar missile guidance since the 1950's,  and has gotten rather good with the advent of sophisticated longer-range autonomous seekers in things like AMRAAM and its Russian counterpart AA-12. That gets you within 1's to 10's of meters of your aimpoint,  and that's good enough. Why would we not use that?  Makes no common sense not to.

So the only shortfall here for precision landing on Mars is a swarm of positioning satellites in orbit about Mars of adequate capability to manage direct-entry trajectories.  We already know how to build them.  We already have heavy lift rockets already that can send them to Mars,  and will soon have an even better one (Falcon-Heavy).  The only thing lacking is somebody bellying up to the bar to pay for doing this (and I bet Musk is already talking to NASA about doing it,  behind the scenes).  You solve that lack by who you vote for,  and who they nominate to lead the agencies.

GW


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#22 2018-04-29 18:27:26

kbd512
Moderator
Registered: 2015-01-02
Posts: 2,957

Re: GPS system for Mars?

Louis,

Good grief.  No.  Just no.

Jet engine experimentation started in the late 1920's.  The first jet aircraft were built during WWII, which started more than a decade later.  Those first jet engines were trashed after a handful of hours of operation.  In the 21st century, nearly a century after the first jet engines were constructed, China and Russia still can't build a jet engine that lasts longer than about a third of the operating life of an American, British, or French built jet engine.  That's just a fact and you can believe what you want.

The atomic bomb didn't leap into existence in WWII.  The basic theory and experimentation required to lay the groundwork for the construction of such a device occurred decades earlier.  Obviously further innovation was required in the run-up to the world's first nuclear weapon.

The lunar landing was the culmination of decades of prior work encompassing everything from materials design, aerospace vehicle design, rocket engine design, computers, and basic mathematics.

The laser communications system that NASA's contractors have developed for them is the result of many years of development and testing efforts.  They'll be ready to use after they've been properly tested, which should be in 2019.

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#23 2018-04-29 18:36:21

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 16,141

Re: GPS system for Mars?

The cash for the cow is going to Nasa and not to others unless Nasa does a Request and contract to develope so unless Nasa is developing its up to the private industry to want to fork out there own cash which may never yield a return on investment.

Spacex is rolling money from other side businesses to make space x developement possible and then turning around and doing the same for its other parts....Nasa is not done that way .
Sure some of the old space are but they are so lathargic from being on the gravy train that they forgot how they got there.

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#24 2018-04-29 19:37:24

Oldfart1939
Member
Registered: 2016-11-26
Posts: 1,714

Re: GPS system for Mars?

It wouldn't be a smart investment for SpaceX to reinvent the wheel, when GPS satellites are concerned. Given the vertical integration of the company, they could manufacture their own based on designs owned by the Air Force. Lockheed Martin seems to have the next contract locked up since Boeing and Grumman Northrup have declined to bid on the next series. Putting a constellation of the satellites in orbit around Mars would, in my mind, be a major step forward w/r landing the BFR/BFS. In my earlier post regarding the need for these satellites, they would not only make the landings more accurate, but allow the incoming space vehicle make the atmospheric entry correctly. W/R the concept of laser communication: that requires tremendous directional pointing ability of the satellites to a fast moving target. Not going to happen that soon. Untested technology and one difficult to implement. Thanks to GW for amplifying the reasoning behind my earlier comments.

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#25 2018-04-30 05:36:49

louis
Member
From: UK
Registered: 2008-03-24
Posts: 4,896

Re: GPS system for Mars?

If you are just going to keep going back, well you could say the Romans had a form of jet engine (the aelopile)...

https://en.wikipedia.org/wiki/Aeolipile

I was talking about projects that were specifically geared to producing a working product (not simply a research project), going from initial approval to completion. I think you will find my timeframe figures are reasonably accurate.

kbd512 wrote:

Louis,

Good grief.  No.  Just no.

Jet engine experimentation started in the late 1920's.  The first jet aircraft were built during WWII, which started more than a decade later.  Those first jet engines were trashed after a handful of hours of operation.  In the 21st century, nearly a century after the first jet engines were constructed, China and Russia still can't build a jet engine that lasts longer than about a third of the operating life of an American, British, or French built jet engine.  That's just a fact and you can believe what you want.

The atomic bomb didn't leap into existence in WWII.  The basic theory and experimentation required to lay the groundwork for the construction of such a device occurred decades earlier.  Obviously further innovation was required in the run-up to the world's first nuclear weapon.

The lunar landing was the culmination of decades of prior work encompassing everything from materials design, aerospace vehicle design, rocket engine design, computers, and basic mathematics.

The laser communications system that NASA's contractors have developed for them is the result of many years of development and testing efforts.  They'll be ready to use after they've been properly tested, which should be in 2019.

Last edited by louis (2018-04-30 05:37:19)


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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