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#101 2018-11-13 19:53:56

Oldfart1939
Member
Registered: 2016-11-26
Posts: 2,306

Re: Journey time to Mars...

Louis-The Ball Astronautics designer of the MRO is a member of our local Mars Society Chapter in Boulder, Colorado. I'll ask him some of these questions in person this coming Monday evening meeting, although Robert Zubrin may be there as well to talk about Moon Direct.

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#102 2018-11-13 19:57:33

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 26,798

Re: Journey time to Mars...

Apollo moon landings were all on the sun lite side with a duration of 14 days before going dark
https://en.wikipedia.org/wiki/Moon_landing
https://en.wikipedia.org/wiki/Apollo_Lunar_Module
The capsule orbit time was 47 minutes before the LM could talk to the capsule but the LM was in contact with the earth all the time.
The crew man that stayed on the capsule experienced lonelyness that was erie from the radio silence.

The crews going to mars will not have all the information for what they came in nor will they have the expertise or parts to make a fix for all things that might fail.

Just look to Apollo 13 for how little time they had to come up with a plan to make it back home...

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#103 2018-11-13 20:03:06

louis
Member
From: UK
Registered: 2008-03-24
Posts: 7,208

Re: Journey time to Mars...

MRO's a relatively small craft compared with the BFS. And once the BFS lands it can unload a much bigger, more powerful  transmitter/dish.

kbd512 wrote:

Louis,

This is about mission control engineering assistance with complex system problems, not real-time monitoring, although the laser data transmission rate is sufficient for a couple of life feeds and mission control's delayed monitoring of vital systems to predict failures.  The laser based systems are clearly far superior to the radio frequency systems, if the subsystem mass, power, and signal quality are considerations.  Most other people seem to think that they are.

MRO can't transmit its own data back in a timely manner, but now we're going to run a mission with humans and robots all over the planet?

Not.


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

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#104 2018-11-13 20:05:35

louis
Member
From: UK
Registered: 2008-03-24
Posts: 7,208

Re: Journey time to Mars...

Night/day cycle on the Moon not much to do with "dark side of the moon" which appears nearly always dark to us on Earth due to synchronised rotation.

SpaceNut wrote:

Apollo moon landings were all on the sun lite side with a duration of 14 days before going dark
https://en.wikipedia.org/wiki/Moon_landing
https://en.wikipedia.org/wiki/Apollo_Lunar_Module
The capsule orbit time was 47 minutes before the LM could talk to the capsule but the LM was in contact with the earth all the time.
The crew man that stayed on the capsule experienced lonelyness that was erie from the radio silence.

The crews going to mars will not have all the information for what they came in nor will they have the expertise or parts to make a fix for all things that might fail.

Just look to Apollo 13 for how little time they had to come up with a plan to make it back home...


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

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#105 2018-11-14 19:49:02

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 26,798

Re: Journey time to Mars...

The radio signals can not go through the moon from the dark side of it as its on the oposite side and not the earth side where signals can make it to earth. The moon is blocking them.

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#106 2018-11-14 20:53:03

kbd512
Administrator
Registered: 2015-01-02
Posts: 6,240

Re: Journey time to Mars...

SpaceNut,

I see that you're running into fundamental understanding problems here as well.  The size of the satellite dish on the transmit side is far less of the problem that Louis thinks it is in comparison to the strength and directionality of the electrical transmission, which is predicated on transmission power, frequency (there's no such thing as a high data rate VLF communications system), and any objects between the transmitter and receiver that obstruct or weaken the signal.  There's all sorts of resources on YouTube that could teach him the subject so that he better understands the problem.  The giant satellite dish he's so fixated on would be superlative for reception of data sent from Earth, would somewhat improve upon the transmission of data sent to Earth from Mars, and yet the overall issue with the strength and quality of the signal received by Earth from Mars would remain.  It's fundamentally a problem with the electrons being sent to Earth, as it pertains to how many electrons and any distortion or change in voltage (energy) values imparted by external effects from the Sun, interstellar radiation sources, and atmospheres between Mars and Earth.

Since there will always be a practical limit to the electrical power a spacecraft can generate and then use to transmit, the solution on the Earth side where the mass of the satellite dishes is of no real consequence, unlike a spacecraft application where weight is absolutely critical, is to make it huge.  There's no practical problem with doing that, since all spacecraft are effectively "phoning home" and only a few commands or responses will be sent saying "message received, now do this".  Lasercom permits very high bi-directional data rate transmissions using comparatively tiny and low power terminals on both ends because the power that the laser requires to transmit is quite low and the data carrier "signal" is an incredibly coherent laser beam that truly is unidirectional, rather than merely directional radio frequency transmission that starts spreading out from the moment the radiated electrical power leaves the antenna.

I still think he doesn't understand the fundamentals of how radios and lasers work, even though an hour's worth of YouTube videos or a quick read through an appropriate website could change that.  Maybe he thinks we're just being argumentative or contrarian, even though I'm only trying to express why things are done the way they are.  I've mostly given up on this topic since we've already hashed out why things are done the way they are and what the salient technological limitations are.  If he won't read up on these things he's proposing, then he simply won't "get" why GW, Oldfart1939, nor you and I respond with what we respond with.

Edited for grammar / usage

Last edited by kbd512 (2018-11-14 20:56:47)

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#107 2018-11-15 03:16:16

louis
Member
From: UK
Registered: 2008-03-24
Posts: 7,208

Re: Journey time to Mars...

I haven't claimed specialist knowledge of engineering radio communications but I note when we chose to send the Arecibo message into interstellar space we did so from a radio telescope with a dish measuring over 300 metres across.

I was simply suggesting there was some relationship between size of dish and ability to send data back to Earth from Mars. I am happy to accept power is the more significant issue.

Here's an interesting part of a discussion regarding this issue:

"However, the Mars Reconnaissance Orbiter also states that this link tops out at 4 megabits per second (worst case is 500 kbps), which leads us to the nail in the coffin:

    Best-case data rates from Mars are on the order of 4 Mbps, whereas compressed-with-H.264 720p video needs 12 Mbps and 1080p needs closer to 22 Mbps. This rate from Mars is only achievable for a few months at closest approach. You would need to increase the link speed by a factor of at least 3 to get live, HD video even then."

https://space.stackexchange.com/questio … 20-mission

What is the problem with running say 4-6 MRO-style set ups in parallel to send back video data? After a period of delay (let's say 30 secs) back on Earth, the whole package could be re-synched to produce perfect video. That, to me, sounds well within our capabilities. The mass involved will also be well within the capability of a Space X 500 tonne cargo mission.

As always we are being told certain things are not possible when I suspect they are perfectly possible. Yes, you can't get over the speed of light issue - there will always be a transmission delay - but the 500 tonne cargo mission to Mars opens up possibilities that haven't existed before.


kbd512 wrote:

SpaceNut,

I see that you're running into fundamental understanding problems here as well.  The size of the satellite dish on the transmit side is far less of the problem that Louis thinks it is in comparison to the strength and directionality of the electrical transmission, which is predicated on transmission power, frequency (there's no such thing as a high data rate VLF communications system), and any objects between the transmitter and receiver that obstruct or weaken the signal.  There's all sorts of resources on YouTube that could teach him the subject so that he better understands the problem.  The giant satellite dish he's so fixated on would be superlative for reception of data sent from Earth, would somewhat improve upon the transmission of data sent to Earth from Mars, and yet the overall issue with the strength and quality of the signal received by Earth from Mars would remain.  It's fundamentally a problem with the electrons being sent to Earth, as it pertains to how many electrons and any distortion or change in voltage (energy) values imparted by external effects from the Sun, interstellar radiation sources, and atmospheres between Mars and Earth.

Since there will always be a practical limit to the electrical power a spacecraft can generate and then use to transmit, the solution on the Earth side where the mass of the satellite dishes is of no real consequence, unlike a spacecraft application where weight is absolutely critical, is to make it huge.  There's no practical problem with doing that, since all spacecraft are effectively "phoning home" and only a few commands or responses will be sent saying "message received, now do this".  Lasercom permits very high bi-directional data rate transmissions using comparatively tiny and low power terminals on both ends because the power that the laser requires to transmit is quite low and the data carrier "signal" is an incredibly coherent laser beam that truly is unidirectional, rather than merely directional radio frequency transmission that starts spreading out from the moment the radiated electrical power leaves the antenna.

I still think he doesn't understand the fundamentals of how radios and lasers work, even though an hour's worth of YouTube videos or a quick read through an appropriate website could change that.  Maybe he thinks we're just being argumentative or contrarian, even though I'm only trying to express why things are done the way they are.  I've mostly given up on this topic since we've already hashed out why things are done the way they are and what the salient technological limitations are.  If he won't read up on these things he's proposing, then he simply won't "get" why GW, Oldfart1939, nor you and I respond with what we respond with.

Edited for grammar / usage

Last edited by louis (2018-11-15 03:25:08)


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

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#108 2018-11-15 11:51:19

kbd512
Administrator
Registered: 2015-01-02
Posts: 6,240

Re: Journey time to Mars...

Louis,

Radio Telescopes

The Arecibo radio telescope is used to detect the faintest of signals from other places in our galaxy.  Its giant size is dictated by a requirement for sensitivity and selectivity.  Why did scientists choose to transmit using that device?  Probably because it's capable of transmitting a signal of exceptional quality.  It'll be years to decades before it's received by the closest stars.

Flying Bricks

I'm not telling you that you can't put more thrust behind a brick to make it fly.  It's obvious that you can, but what do you get in return?  I'm telling you that if the brick is shaped like a bullet and you put large enough wings on it to generate sufficient lift, then even though it's not a very good aerospace vehicle it'll fly a whole lot better than if you simply put more thrust behind it, if economy of force is any consideration.  There's a massive penalty to the "just use more thrust" argument that only gets worse as the brick gets heavier, increases in size, or as more performance (speed) is demanded from the brick-shaped aerospace vehicle.

Satellite Transceiver Performance

Regarding your example of running a MRO-type satellite with multiple antennas on it, there's no technical problem with doing that.  Our military and commercial communications satellites routinely use multiple transceiver dishes.  It's a lot more useful than a single giant satcom dish.  The data transfer rate problem is "solved" in two principle ways.  The first is the use of higher frequency operation that increase the number of cycles per second that the system's carrier signal can use to stuff more data into and the second is to increase the quality of the signal processing electronics to make them more sensitive and selective.  Within the limitations of a frequency range dictated by other factors such as the radios in common use, it's quite common to use multiple transceiver arrays / dishes that permit multiple simultaneous send / receive channels.  The Ka-band stuff NASA is implementing is a microwave frequency solution that's capable of giving you that HD live streaming video feed.

When the military needs a more sensitive satellite transceiver, then they use the "giant satellite dish" method of achieving that objective if the system is mounted to a naval ship or Mother Earth.  It has the side effect of increasing data transfer rates, within the limitations of the system, but only because the signal quality is better and only by so much.  When the military needs higher sustained data transfer rates, they use multiple higher frequency systems with better signal processing electronics.  The government contractor's solution to the "give us a bigger pipe" problem posed by our military has always been higher frequency operation and better signal processing.  The use of lasers and microwaves is the ultimate form of higher frequency operation.

Judicious Use of Available Tonnage

In a crewed Mars mission where there are endless demands on delivered tonnage, why would your solution to a communications data rate problem be to use a single giant satellite dish when multiple smaller higher frequency systems would easily outperform the single larger system, both individually and in aggregate, and provide a level of redundancy that's impractical with the larger system?

It's perfectly possible to use up all 500t of the cargo allotment with a giant satellite dish, but then there are no consumables for humans on Mars, just a giant satellite dish with no one to use it.

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#109 2018-11-15 11:54:50

JoshNH4H
Member
From: Pullman, WA
Registered: 2007-07-15
Posts: 2,526
Website

Re: Journey time to Mars...

kbd512 wrote:

It's perfectly possible to use up all 500t of the cargo allotment with a giant satellite dish, but then there are no consumables for humans on Mars, just a giant satellite dish with no one to use it.

lol


-Josh

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#110 2018-11-15 13:09:17

louis
Member
From: UK
Registered: 2008-03-24
Posts: 7,208

Re: Journey time to Mars...

When did I argue for a "giant" satellite dish on Mars. Never! A more sizeable dish is what I referenced.  If a system of multiple MRO transceivers can do the job of streaming HD video, that's good enough for me. The whole of the MRO weighs only a tonne. I doubt the transceiver is more than 20% of the mass. So 6 of them would be no more than 1.2 tonnes. Communications is a key priority - 1.2 tonnes out of 500 tonnes is hardly breaking the bank.

kbd512 wrote:

Louis,

Radio Telescopes

The Arecibo radio telescope is used to detect the faintest of signals from other places in our galaxy.  Its giant size is dictated by a requirement for sensitivity and selectivity.  Why did scientists choose to transmit using that device?  Probably because it's capable of transmitting a signal of exceptional quality.  It'll be years to decades before it's received by the closest stars.

Flying Bricks

I'm not telling you that you can't put more thrust behind a brick to make it fly.  It's obvious that you can, but what do you get in return?  I'm telling you that if the brick is shaped like a bullet and you put large enough wings on it to generate sufficient lift, then even though it's not a very good aerospace vehicle it'll fly a whole lot better than if you simply put more thrust behind it, if economy of force is any consideration.  There's a massive penalty to the "just use more thrust" argument that only gets worse as the brick gets heavier, increases in size, or as more performance (speed) is demanded from the brick-shaped aerospace vehicle.

Satellite Transceiver Performance

Regarding your example of running a MRO-type satellite with multiple antennas on it, there's no technical problem with doing that.  Our military and commercial communications satellites routinely use multiple transceiver dishes.  It's a lot more useful than a single giant satcom dish.  The data transfer rate problem is "solved" in two principle ways.  The first is the use of higher frequency operation that increase the number of cycles per second that the system's carrier signal can use to stuff more data into and the second is to increase the quality of the signal processing electronics to make them more sensitive and selective.  Within the limitations of a frequency range dictated by other factors such as the radios in common use, it's quite common to use multiple transceiver arrays / dishes that permit multiple simultaneous send / receive channels.  The Ka-band stuff NASA is implementing is a microwave frequency solution that's capable of giving you that HD live streaming video feed.

When the military needs a more sensitive satellite transceiver, then they use the "giant satellite dish" method of achieving that objective if the system is mounted to a naval ship or Mother Earth.  It has the side effect of increasing data transfer rates, within the limitations of the system, but only because the signal quality is better and only by so much.  When the military needs higher sustained data transfer rates, they use multiple higher frequency systems with better signal processing electronics.  The government contractor's solution to the "give us a bigger pipe" problem posed by our military has always been higher frequency operation and better signal processing.  The use of lasers and microwaves is the ultimate form of higher frequency operation.

Judicious Use of Available Tonnage

In a crewed Mars mission where there are endless demands on delivered tonnage, why would your solution to a communications data rate problem be to use a single giant satellite dish when multiple smaller higher frequency systems would easily outperform the single larger system, both individually and in aggregate, and provide a level of redundancy that's impractical with the larger system?

It's perfectly possible to use up all 500t of the cargo allotment with a giant satellite dish, but then there are no consumables for humans on Mars, just a giant satellite dish with no one to use it.


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

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#111 2018-11-15 17:26:52

Oldfart1939
Member
Registered: 2016-11-26
Posts: 2,306

Re: Journey time to Mars...

Louis-
I will be attending the meeting of the Rocky Mountain Mars Society, Boulder, Colorado this coming Monday night. If Jim is there, I'll ask him about the MRO transceiver mass, since he designed the whole damned thing! But for your edification, the MRO is now an ageing piece of equipment that is still operating because of the robustness of the design and excellent construction. I know it stuns many of our guest speakers to be unloaded on about the capabilities that blithely, they really don't know in sufficient detail, to talk about.

Last edited by Oldfart1939 (2018-11-15 21:46:49)

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#112 2018-11-15 17:56:36

louis
Member
From: UK
Registered: 2008-03-24
Posts: 7,208

Re: Journey time to Mars...

That would be great!

Ask him about having a series of (updated) MRO transceivers in place on the surface of Mars (6 or more) as a way of transmitting HD live video from Mars.

Oldfart1939 wrote:

Louis-
I will be attending the meeting of the Rocky Mountain Mars Society, Boulder, Colorado this coming Monday night. If Jim is there, I'll ask him about the MRO transceiver mass, since he designed the whole damned thing! But for your edification, the MRO is now an ageing piece of equipment that is still operating because of the robustness of the design and excellent construction. I know it stuns many of our guest speakers to be unloaded on about the capabilities that blithely, they really don't know in sufficient detail to talk about.


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

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#113 2018-11-15 17:58:46

kbd512
Administrator
Registered: 2015-01-02
Posts: 6,240

Re: Journey time to Mars...

Louis,

Incidentally, MRO was the test platform for Ka-band operation.  It's returned more data than all other Mars missions combined and is the primary reason some of them can return their data in a useful way.  A Lasercom-equipped MRO could return approximately 200 times more data using the same electrical power.  Imagine being able to shove a HiRISE image down the pipe every few seconds instead of 1.5 hours.

Magellan returned 3,740 gigabits of data.  MRO has returned tens of terabits and counting.

Here's a copy of the document about MRO's communication system with Jim Taylor's name on it:

Mars Reconnaissance Orbiter Telecommunications by Jim Taylor, Dennis K. Lee, and Shervin Shambayati

Edit: Apparently, MRO returned 264 terabits of data from 2006 to 2016 and served as the landing scout site for 7 subsequent missions.  That's only 33TB.  Imagine what you could do with a pipe 200 times wider.  NASA would need a data center dedicated to storing the deluge data returned from their science missions.

Edit 2: JPL's discussion of an upgraded MRO replacement

The Space Review - A coming communications crunch at Mars by Cody Knipfer - Jun 5, 2017

MEPAG Next Orbiter Science Analysis Group (NEX-SAG) - Overview of the Final Report - March 2, 2016

Edit 3: MSL's communications system

Mars Science Laboratory Communications System Design by Andre Makovsky, Peter Ilott, and Jim Taylor

Last edited by kbd512 (2018-11-15 19:55:52)

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#114 2018-11-15 20:54:12

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 26,798

Re: Journey time to Mars...

The dish for communications is a parabolic reflector that concetrates the very low level signal over its area to the feed horn that allows for the signal strength to go up to then be amplified for detection in recieving mode. For transmitting the fed horn send the signal bouncing off the reflecting surface widening the beam for a greater window of possible reception at the target location so that it can be recieved.

.

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#115 2018-11-15 21:18:22

kbd512
Administrator
Registered: 2015-01-02
Posts: 6,240

Re: Journey time to Mars...

SpaceNut,

To answer the question Louis had, the 3 meter HGA for the Ka-band transceiver aboard MRO weighs 19.1kg and consumes 81W of power.  It's in the MRO telecom document I posted.  MRO's total telecom subsystem mass was 107.7kg and designed to use 359W of power.  The Lasercom system is designed to use 78W of power in total, 4W going to the laser, and transfer 311 times more than the actual achieved transfer rate when Mars is closest to Earth.  The entire Lasercom system is supposed to weigh 28kg, as compared to the Ka-band dish and related components, which weigh a total of 45kg.  The 200 times more data figure that I cited uses MRO's theoretical data transfer rate (never actually achieved).  Recall that the first Lasercom test actually achieved its target data transfer rate of 622mbps and the new system approximately doubles that demonstrated capability.

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#116 2018-11-16 01:49:40

louis
Member
From: UK
Registered: 2008-03-24
Posts: 7,208

Re: Journey time to Mars...

Thanks kbd, so even with 6 of them, perhaps sturdier surface versions,  and maybe increased power transmission, we are talking about  a v. minimal amount of mass - less than 1 tonne for sure. 

We must be able to produce live HD video from Mars, even 3D. This will be an absolute revelation for people back on Earth.

kbd512 wrote:

SpaceNut,

To answer the question Louis had, the 3 meter HGA for the Ka-band transceiver aboard MRO weighs 19.1kg and consumes 81W of power.  It's in the MRO telecom document I posted.  MRO's total telecom subsystem mass was 107.7kg and designed to use 359W of power.  The Lasercom system is designed to use 78W of power in total, 4W going to the laser, and transfer 311 times more than the actual achieved transfer rate when Mars is closest to Earth.  The entire Lasercom system is supposed to weigh 28kg, as compared to the Ka-band dish and related components, which weigh a total of 45kg.  The 200 times more data figure that I cited uses MRO's theoretical data transfer rate (never actually achieved).  Recall that the first Lasercom test actually achieved its target data transfer rate of 622mbps and the new system approximately doubles that demonstrated capability.

Last edited by louis (2018-11-16 01:51:24)


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

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#117 2018-11-16 05:04:32

elderflower
Member
Registered: 2016-06-19
Posts: 1,262

Re: Journey time to Mars...

Since when did one tonne become minimal mass. I know the BFR is much bigger than previously proposed vehicles, but mass is still a major issue. If you want to put a large satellite into Mars orbit, it will have to be sent on a different solar orbit from the BFR which is going direct to the surface. That means a separate vehicle with its own rocket stage and propellant.
I would also query the need for live feeds. Everything will be delayed by transmission time. Acceptable in the case of the moon, but not at Mars. You may as well record it and squirt it back when conditions are appropriate, especially so if you aren't using relay satellites. You wont be able to transmit or receive from the surface when Earth is not visible.

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#118 2018-11-16 08:18:58

louis
Member
From: UK
Registered: 2008-03-24
Posts: 7,208

Re: Journey time to Mars...

I wasn't suggesting we put a new satellite in orbit. I was suggesting we have a ground station for direct contact with Earth.

Live feeds are what will make huge money as news organisatons pay for exclusive access. They raise the level of excitement.

elderflower wrote:

Since when did one tonne become minimal mass. I know the BFR is much bigger than previously proposed vehicles, but mass is still a major issue. If you want to put a large satellite into Mars orbit, it will have to be sent on a different solar orbit from the BFR which is going direct to the surface. That means a separate vehicle with its own rocket stage and propellant.
I would also query the need for live feeds. Everything will be delayed by transmission time. Acceptable in the case of the moon, but not at Mars. You may as well record it and squirt it back when conditions are appropriate, especially so if you aren't using relay satellites. You wont be able to transmit or receive from the surface when Earth is not visible.


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

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#119 2018-11-16 13:47:19

kbd512
Administrator
Registered: 2015-01-02
Posts: 6,240

Re: Journey time to Mars...

Louis,

Communications Done Right

Relay to an orbital satellite that's unaffected by ground conditions is still the right way to do communications.  That's the way it's done here on Earth, by both militaries / scientific entity / private sector, and that's the way it's currently done on Mars.  There are practical signal attenuation problems associated with transmission directly to Earth from the surface of Mars, such as the day / night cycle, dust storms, and orbital phases.  It's not that it's impossible to do, it's just a highly inefficient means to communicate.  MRO is over Curiosity for just 8 minute per orbit and in those 8 minutes Curiosity relays as much data (250mbits / day, according to the MSL communications document I posted) through its onboard X-band satcom transceiver to MRO for re-transmission to Earth as the same system could relay to Earth from the surface of Mars over a period of 20 hours.

RF vs Laser Mass and Power Consumption

I would expect that an actual portable Ka-band satcom unit with a half dozen antennas that only needs to communicate with an orbiting next generation MRO type satellite would weigh a matter of a few tens of kilograms at most because an antenna with sufficient gain would be tiny in that specific use case.  MSL's X-band HGA weighs 1.4kg, the gimbal mechanism is 6.6kg, and the associated microwave transceiver set components weigh 3.7kg.  That's a total of only 11.7kg for a reasonably high-speed uplink to MRO (HD streaming video would require a Ka-band array or Lasercom system).  A Ka-band system would have similar weight (because as you can see, weight is driven by everything else besides the actual satcom antenna) and less power consumption (driven by the output power of the radio and the DSP electronics).

X-band is 8GHz to 12GHz (3.75cm to 2.5cm wavelength) - Viking landers, Voyager, Galileo, New Horizons, Cassini-Huygens, MSL / Curiosity satcom, ExoMars

Ka-band is 26.5GHz to 40GHz (1.11cm to 7.5mm wavelength) - MRO satcom, MSL EDL radar, Inmarsat I-5, Iridium Next, and James Webb Space Telescope

NASA Lasercom is 193THz (1550nm wavelength) - LCRD, LLCD / LADEE, ISS, Orion EM-2, Psyche

NASA's Future Space Optical Networks

NASA’s Optical Communications Program for 2017 and Beyond

NASA is currently working on a Gen-2 Lasercom system that can support transfer rates of up to 200gbps (>56tbps / day or 7 terabytes per day) using COTS telecom components taken from American industry.  The integrated photonics optical modems are approximately 1.5 times the size of a deck of playing cards, rather than the shoebox sized devices in current use.  The space-based laser relays will be a series of 2U micro satellites.  The ground infrastructure will consist of high-end amateur astronomy telescopes (apparently the optics are good enough to support transfer up to 60tbps / day), rather than specialized equipment.  Incidentally, I was correct in my assertion that NASA would need to open a data center, as that's also part of the plan.

The current state-of-the-art Optical User Terminal (OUT) for the Psyche-16 mission weighs 36kg and consumes 100W of power.  They intend to build 5 of the 2U microsats and 5 of the Gen-1 OUT's to use with near-Earth and asteroid missions.  The Gen-2 systems aboard the microsats are expected to consume <10W of power.

The first missions to Mars could be live-streamed in 5K 60p, rather than 1080p.  A 5,120x2,160 (5K) resolution at 60 frames per second (60p) with a 16 bit color depth and 4:4:4 chrome sampling correlates to a data transfer rate of 44.55gbps.  If you want to "go for the gold" and broadcast in 10K (all other characteristics the same), that's 178.2gbps.  The landing could also be pre-recorded, uploaded, and buffered through the deep space optical network.  Those 2U microsats have 2TB buffers, so maybe the buffer size should be increased.

Portable Satcom Transceivers from the Last Decade

The high frequency satcom antennas we had in the military a decade ago could literally be lifted or re-pointed with one finger, which is why they were problematic for use aboard ship, since wind and ocean spray would easily topple them without weight on top of the legs.  During exercises, they were frequently set up on the helo deck.

The radio or satcom transceiver set that was attached to the antenna, or what we called "green gear" (Army and Marine Corps portable field radios and satcom transceiver sets, which were also used as backup equipment by the Navy, are painted green), was many times the weight of the antenna itself, yet the radio could still be lifted with one finger through one of the handles.  The batteries were the heaviest part, but we had ship's power so that was never an issue for us.

Any extra mass for a Mars variant of these of X-band, Ka-band, and Lasercom technologies that have been in military use for well over a decade would be related to thermal insulation and regulation, extreme precision gyros, batteries, and solar power.  The Electra Lite radios / transceivers on MRO and MSL look like "gold gear" to me, or Titanium Nitride coated versions of the green CARC painted stuff we used.

The antenna looked almost exactly like the one in this photo from General Dynamics, but the laptop is new and the transceiver itself (still a piece of green gear, apparently) is much smaller:

SATCOM Base Station

Ours didn't have the laptop, but I recall receiving some new toys that came with a laptop as T&E equipment.  I guess it's standard issue now.  Both the terminal (like a laptop, but purpose-built for communications only) and transceiver set of the time were pieces of green gear like the transceiver shown in the photo from GD-MS.

The latest military, space, and amateur radios use SDR (Software-Defined Radio) technology.  The data handling is done by the laptop, iPad, or iPhone.  The radio or satcom transceiver is a little box that only has to take the encoded data output from the laptop as input and generate RF power in the correct frequency range to the antenna.  Prior to spectacularly powerful and efficient general purpose processors, that was done by expensive specialty chips inside the radio.

I believe both MRO and MSL use SDR's so that any required tweaks to the radio to improve processing performance can be uploaded as new software and then used without any modifications to the hardware.  The compute capabilities of the iPhone and Android are mind blowing to a person like me who grew up making radios and constantly modifying hardware on breadboards to change the operation of the radio.  Anyway, modern microelectronics and SDR are wonderfully powerful things.

Edit: Nevermind, I found the exact piece of gear we had:

AN/PSC-5 SPITFIRE Satellite Radio Terminal

I see that a later version of this piece of equipment also incorporated SDR technology.  Anyway, you can see from the photo how rinky-dink that antenna assembly was.  This was the backup to the "giant satellite dish", and it featured a higher data transfer rate, too.

Last edited by kbd512 (2018-11-16 13:58:56)

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#120 2018-11-16 14:36:40

Oldfart1939
Member
Registered: 2016-11-26
Posts: 2,306

Re: Journey time to Mars...

The major problem that I can see is we need roughly 8 GPS satellites in MO, just in order to nail down landing accuracy. These could certainly incorporate communications capacity, given the mass allowances required for one by Lockheed-Martin. key assumption in the SpaceX landing plans for Mars surface accuracy is3 GPS satellites, plus a ground-based transponder system.

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#121 2018-11-16 14:36:50

JoshNH4H
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From: Pullman, WA
Registered: 2007-07-15
Posts: 2,526
Website

Re: Journey time to Mars...

Here's a general thought:

There's a huge difference between an organization or project with large resources and one with unlimited resources.

An organization with large resources will invest them to improve itself and have more resources and capabilities in the future.

An organization with unlimited resources won't: When it encounters a problem it will simply throw more money and manpower at it until it goes away.

One thing louis likes to say when faced with a critique of one of his plans (for example: artificial lighting for greenhouses consumes an obscene amount of power) is that he believes there will be an abundance of electrical energy on early Mars.  This is a good example of "unlimited resource" thinking.  "Build a bigger satellite dish" is another example.

In louis's defense, he does not claim specific technical knowledge that he doesn't have.  His broader point, that it's possible to get higher data rates, is not wrong, although it's also not particularly insightful.


-Josh

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#122 2018-11-16 17:38:36

louis
Member
From: UK
Registered: 2008-03-24
Posts: 7,208

Re: Journey time to Mars...

I think that - better than some perhaps - I conceive of the overal Mars project as requiring different approaches at different times on the development of the settlement. Indoor artificially lit agriculture makes sense when you have a population of 100 or even 1000. It doesn't make sense if you have a population of 100,000 or 1 million.

I argued for a somewhat larger dish than the one used in the Apollo Mission - not for a giant dish. I now think the best approach is a ground station of interconnected smallish transceivers like the one used with the MRO. Perhaps 6 of them to allow for live HD video.

Yes it's possible to get higher data rates, and I didn't think that was a particularly difficult objective. My point is much more that people don't seem to make the connection - that a Space X mission is going to offer us stunning live video colour views of Mars.







JoshNH4H wrote:

Here's a general thought:

There's a huge difference between an organization or project with large resources and one with unlimited resources.

An organization with large resources will invest them to improve itself and have more resources and capabilities in the future.

An organization with unlimited resources won't: When it encounters a problem it will simply throw more money and manpower at it until it goes away.

One thing louis likes to say when faced with a critique of one of his plans (for example: artificial lighting for greenhouses consumes an obscene amount of power) is that he believes there will be an abundance of electrical energy on early Mars.  This is a good example of "unlimited resource" thinking.  "Build a bigger satellite dish" is another example.

In louis's defense, he does not claim specific technical knowledge that he doesn't have.  His broader point, that it's possible to get higher data rates, is not wrong, although it's also not particularly insightful.


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

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#123 2018-11-16 17:48:22

kbd512
Administrator
Registered: 2015-01-02
Posts: 6,240

Re: Journey time to Mars...

Oldfart1939,

If you read that MEPAG doc I linked to in Post #113, JPL basically wants to build a Gen-2 MRO incorporating the following:

* 1m+ class telescope using a multi-gigapixel CCD

HiRISE has a 504 megapixel CCD, but cameras with 400 megapixel CCD's are now available from Hasselblad for digital archiving for about $48K and multi-gigapixel imagers are now in common use in military aerial drones and in astronomy

* ground penetrating radar powerful enough to accurately map ice deposits from orbit

SHARAD was a good start

* characterize surface ice and mineral deposits

two of the three cryocoolers for CRISM have now failed

* characterize atmospheric processes

MARCI and MCS was a good start

* map surface brine flows

CTX was a good start

JPL's desire is to take our understanding of Mars to the next level by compiling extremely accurate maps of the atmosphere, surface, and subsurface.  I see no reason why we shouldn't also incorporate the latest and greatest communications and positioning equipment into the same platforms.  Falcon 9 Heavy could TMI pairs of the Gen-2 MRO's per flight, whereupon SEP would take over the propulsion requirements.

Besides, MRO is rapidly aging:

Mars Reconnaissance Orbiter Preparing for Years Ahead

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#124 2018-11-16 21:48:36

Oldfart1939
Member
Registered: 2016-11-26
Posts: 2,306

Re: Journey time to Mars...

kbd512-
Yes, I agree that MRO is dying--and pretty rapidly. If we're serious about "going there," then it's time to start investment in some orbiting and planetary based infrastructure. This JPL proposal is spot-on, but the key to resolution is a combination of aperture and the sensors. The sensors in MRO once thought great and state of the art, are now hopelessly obsolescent. Jim at Ball Aerospace will readily admit that; however, we're still getting data, albeit not as detailed as now needed, and at a slower rate than optimal.

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#125 2018-11-16 21:55:41

kbd512
Administrator
Registered: 2015-01-02
Posts: 6,240

Re: Journey time to Mars...

Louis,

I'll try to simplify this, but the entire reason to "build a bigger satcom dish" is:

1. to enhance sensitivity - the receiver's ability to differentiate the desired signal from other noise or interference signals

An antenna's overall efficiency, typically measured in decibels, is a description of an antenna's electrical efficiency and directivity.  Taken together these two attributes represent the gain of an antenna.  High gain antennas have high electrical efficiency and directivity.  Directivity is, as the name suggests, the measure of the antenna's ability to receive signal from a distant emitter and reject interference signals coming in from other directions.  Electrical efficiency is the measure of the antenna's ability to soak up the radiated power from the distant emitter and send it to the receiver's electronics for further processing.

2. to enhance selectivity - the ability to isolate RF radiation of a specific frequency from RF radiation coming in at other frequencies very close to the one you wish to receive on

This is actually determined by the quality of the electronics and software in the receiver, not the antenna itself, but the receiver's ability to be selective is largely predicated on the antenna's ability to be sensitive to received RF power.  Therefore, an antenna that isn't very sensitive will result in a receiver that can't be very selective because whatever the receiver receives from the insensitive antenna is largely predicated upon on which signal happen to be the strongest.  If the desired signal is the strongest, then great.  If not, that's a problem.

3. Bit Error Rate (BER) reduction - in digital communications, which is the application we've been discussing here, overlapping noise or interference signals increase the rate of error associated with reception of transmitted data signals

A very desirable side effect of a sensitive high gain antenna coupled to a highly selective receiver is a significant reduction in BER.  That affects how many bits of data that must be retransmitted because it reduces the number of pieces of the original transmission that were lost or garbled due to overlapping noise or interference.

The satcom dishes on Earth are so big because all spacecraft are severely mass / power limited and most of the data transmission is from the spacecraft back to Earth, rather than from Earth to the spacecraft.  In the event that we needed to assure communications from Earth to the spacecraft using Earth-based transmitters, we'd just put more power behind the transmission signal because there's no significant penalty associated with doing that.  The same is true of the satcom dish size for Earth-based receivers.  In the case of the spacecraft, we have to get more efficient with how we use available mass and power.  At a certain point, the operating frequency of the system also affects data transmission rates to a far greater extent than the size of the transmitter or receiver or available power.  There's only so much data that you can stuff into a carrier signal with a given number of cycles per second.

The 1550nm laser system is operating at just over 193 trillion cycles per second.  The Ka-band system is operating at up to 40 billion cycles per second (any lesser or greater number of cycles per second than the frequency range given in Post #119 and it's no longer Ka-band, it's something else, like X-band or UHF or VHF or whatever).  That's an absolutely enormous difference when it comes to how fast we can shove our data, error correction code, and other meta data out the door.  The laser emitter completes 4,825 times the number of cycles per second in comparison to a 40GHz Ka-band emitter.  Imagine that you had 4,825 40GHz Ka-band transmitters pumping out data simultaneously.  With the 1550nm laser, that's more or less what you have.  It's obviously not that simplistic, but you get the point.

Earth, Mars, and space are vastly different environments for telecommunications, though.  Airborne particulates in the Martian atmosphere can attenuate signals from lasers, but has comparatively little effect on microwaves (X-band and Ka-band, for example).  Moisture in Earth's atmosphere can attenuate both laser radiation and some Ka-band signals.  Space has very little in the way of particulate matter to impede the transit of photons going from Mars orbit to Earth orbit, so they can travel quite some distance with very little attenuation.  That was actually tested by NASA by firing the laser into the stream of photons, electrons, and ions emitted by our Sun in an attempt to mess it up.  Conversely, the electrons and ions thrown off by the Sun can severely affect microwave transmissions (not all the time, obviously, but CME's/SPE's and close proximity to the Sun can severely disrupt RF transmissions from both particle emissions and electromagnetic events).  The job of the radios, irrespective of what wavelength they're operating over, is to contend with that interference and still transfer an acceptable signal.

Anyway, I think the communications topic has been beaten to death at this point.

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