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Dec 4th News Conference
djellison
post Dec 7 2008, 07:28 PM
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QUOTE (peter59 @ Dec 6 2008, 10:55 AM) *
I know that I can be banned by Doug due spreading defeatism.


You can be banned by any admin for breaking the forum rules. Being a realist isn't a crime. ANY mission in extended ops is at risk at any time. $400m over the, I think, 5 years that Doug Mc. described at the press conference, however, shouldn't lead to mission termination's. I believe Ed Weiler has gone on record saying MER wouldn't be a victim however. I can't find it - but I do remember it. MSL may change things, but I doubt it. DSN time is negligible given that downlink is almost exclusively on the back of MRO/MODY downlink anyway, and the DSN almost always has one asset mars pointed. It could be mega-cheap if they rode on the back of MRO given it's high downlink speed would mean even at MRO's lowest downlink rate, and a really good MER pass, it would take less than 4 minutes. ( 150mbits at 0.7mbps). Not sure how MER pays for relay and downlink - perhaps as a percentage of total downlink multiplied by DSN cost for the relaying spacecraft.
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dvandorn
post Dec 8 2008, 04:35 AM
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I just went looking for a rate table of DSN fees, and found the following item in a .pdf file ( http://deepspace.jpl.nasa.gov/advmiss/docs...MEX_AO_2007.pdf ) that describes, among other things, the services and rates for the DSN. There was no actual rate chart; there was a formula for calculating what is called the Aperture Fee:

AF = RB [AW (0.9 + FC / 10)]
where:
AF = weighted Aperture Fee per hour of use.
RB = contact dependent hourly rate, adjusted annually ($1057/hr. for FY08).
AW = aperture weighting:
= 0.80 for 34-meter High-Speed Beam Waveguide (HSB) stations.
= 1.00 for all other 34-meter stations (i.e., 34 BWG and 34 HEF).
= 4.00 for 70-meter stations.
FC = number of station contacts, (contacts per calendar week).

The weighting factor seems to be a multiplier based on a function of aperture size (34m vs. 70m) and number of weekly contacts. An accompanying chart shows the weighting factor for a 70m dish used 28 times per week (i.e., 4 times per day), for example, is 15. The same dish used 14 times a week (twice a day) has a weighting multiplier of a little more than 9. The same numbers of weekly contacts using a 34m dish give you weighting mutiplier of 9 for 28 contacts and 2.5 for 14 contacts.

So, a probe that requires four comm passes a day using a 70m dish looks like it would cost something on the order of $15,865 per hour. That's 28 times $15,865 per week, times 52 per year. That would be $444,220 per month, and $23,990,440 per year. That's based on a reading of the chart, not by plugging numbers into the above formula.

A twice-a-day contact through a 70m dish, again based on the chart, would cost $9,500 or so per comm pass, times 14 passes per week ($133,000), for an annual cost of $6,916,000.

And that all assumes that you're only paying for a single hour of DSN time per pass. In actuality, with calibration times, you're likely going to have pay for a minimum of two hours' worth per pass, possibly more (*). So you might have to double those numbers.

However you slice it up between the various data sources coming through on a MODY or MRO comm pass, total DSN costs add up to millions of dollars a year. So I still think one of the biggest chunks (if not the biggest) of mission operations, extended or otherwise, is DSN time.

-the other Doug

* -- the assumption that each comm pass lasts *at least* an hour is built into the rate structure, I think. At least it says in there: "A station contact may be any length but is defined as the lesser of the spacecraft’s view period, the scheduled pass duration plus calibration times, or 8 hours. For a standard pass, a 45-minute set-up and a 15-minute tear-down time must be added to each scheduled pass to obtain the station contact time (other calibration times apply to Beacon Monitoring and Delta-DOR passes). Note that scheduled pass-lengths should be integer multiples of 1-hour." So even if your comm pass only lasts 12 minutes, it doesn't look like you get the benefit of a pro-rate... dvd


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djellison
post Dec 8 2008, 08:45 AM
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QUOTE (dvandorn @ Dec 8 2008, 04:35 AM) *
So even if your comm pass only lasts 12 minutes, it doesn't look like you get the benefit of a pro-rate...


We've discussed those figures some time ago when talking about discovery missions.

You're not thinking about it properly though - Mars is somewhat unique in that it's almost always locked up with one dish or another. The comms pass will be a 7 hour downlink from MRO and MODY (some of the antennae can and do listen to multiple missions at once) A tiny chunk of that downlink will be MER's - piggybacked on a much much longer session for MODY or MRO. I don't think you can take the generic formula and apply it to MER in that simple a fashion, or indeed any Mars mission. Yes - the DSN costs for MER are not negligible. BUT - they're simply chipping in with a DSN cost that's already there anyway for other Mars missions. The total cost to the Mars Program for DSN costs if you dropped MER would not, I would have thought, drop much, if at all. There's still going to be near continuous downlink from MRO and MODY (and occasionally MEX - although New Norcia and Madrid handle that mostly now). You can't suggest they bill MER for repointing at Mars for each daily downlink when there's a dish already pointing at Mars, and already locked up on the spacecraft that going to do the relay.

Something like Cassini - yeah - take that formula and the schedules and you can find out. The Mars program is more complex than that. How the bill is split up between the missions, we don't know. MER will be paying a lot LOT less than if it were on its own at Mars (which is what your maths infers)
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dvandorn
post Dec 8 2008, 02:03 PM
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Oh, agreed. And obviously, according to the formula itself, the amount of time charged for each chargeable comm pass is a maximum of 8 hours per day ("the lesser of the spacecraft’s view period, the scheduled pass duration plus calibration times, or 8 hours"). MER DTE sessions would be liable for the full cost of such a comm pass, obviously, but that's a tiny fraction of the communications with the rovers. (It's hard from the information I found to tell how much of the calibration times are required for each Mars asset pass even though your dish is already pointed at Mars; I imagine some of that calibration time is necessary each time you shift from one asset to another, but again we don't have enough operational detail to tell for sure.)

The important information missing is the prorate of relay DSN costs that are passed on to the MERs. But you're absolutely right in this case -- you wouldn't be saving any of that money, since you'd be using pretty much the same amount of DSN time whether or not the MERs are reporting data through the relays. You'd have to cancel one or more of the orbiter DSN passes per day (or simply cancel the extended missions of MODY or MRO entirely) in order to save any money from the DSN side of things, and since that would, in effect, be canceling the extended missions of the orbiters *and* the rovers, I don't see that happening. That's too much loss of bang per buck saved. And I, for one, would be pretty durned uncomfortable with a decision to put one or both orbital assets into "cold storage" for several years just to save the DSN charges.

So, as you've noted, it's unlikely that NASA will cancel or curtail the extended missions of MER-A, MER-B, MODY or MRO to find the extra money needed for MSL. I think a delay of MAVEN is more likely, but it's hard to say. We really just need to see what the numbers come out like over the next several months; speculation at this point as to what might be cut or delayed isn't very useful, since we don't have enough information yet to make intelligent guesses.

-the other Doug


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ilbasso
post Dec 8 2008, 03:24 PM
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Maybe USMF members can all point their satellite TV dishes at Mars twice a day and form a collective DSN. Take distributed computing to the next level!!!

wink.gif


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RoverDriver
post Dec 8 2008, 04:04 PM
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QUOTE (ilbasso @ Dec 8 2008, 07:24 AM) *
Maybe USMF members can all point their satellite TV dishes at Mars twice a day and form a collective DSN. Take distributed computing to the next level!!!

wink.gif



Neat idea. Unfortunately most of the LNBs in typical TV satellite systems have a C/N figure that would make it extremely difficult.

Paolo


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ilbasso
post Dec 8 2008, 08:04 PM
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No, I didn't think this was physically possible, but wouldn't it be great if it were!

It's hard to fathom how expensive the DSN charges are - interesting analysis, oDoug. That's the tradeoff for putting lightweight/low wattage transmitters and receivers in the spacecraft. It never ceases to amaze me that we can still pick up Voyager signals from so far out in the Solar System, with only a 20-watt transmitter on the spacecraft.


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imipak
post Dec 8 2008, 09:14 PM
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Per "The Problem With Wikipedia" ( http://xkcd.com/214/ ) : LNBC , C/N ratio (I think?) , satellite dish, Allen Telescope Array ...as they used to say in South Park, "I've learned something today". Not sure I'll be able to recall it tomorrow though wink.gif


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RoverDriver
post Dec 9 2008, 12:06 AM
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Suppose you are in your livingroom and want to hear the birds in the park 2mi away. It is a nice and quiet summer night big windows open, cup your hands near your ears. That's DSN.

Suppose you are in your livingroom and want to hear the same birds 2mi away. It is Thanksgiving, your grandma's hearing aid batteries are low and she is shouting at you. Your relatives try to explain to her she is shouting and start to shoult as well. The kettle in the kitchen is whistling, the door bell rings, the dog starts barking, your newborn triples start crying. That's your TV dish/LNB/reciver. The only reason your TV can receive the satellite signals is beacause the birds in the park are now using a 500KW rock concert PA system.

Paolo


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Disclaimer: all opinions, ideas and information included here are my own,and should not be intended to represent opinion or policy of my employer.
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ElkGroveDan
post Dec 9 2008, 12:41 AM
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Perfect example Paolo! (you crack me up).


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If Occam had heard my theory, things would be very different now.
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Pando
post Dec 9 2008, 03:57 AM
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Paolo, you just made my day...
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Guest_Oersted_*
post Dec 10 2008, 11:03 PM
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Guests






2 years delay = 2 MSL´s?

I am sure they can scrounge together some engineering parts, copy the rest and book an extra place on a rocket by then... smile.gif
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djellison
post Dec 11 2008, 07:59 AM
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QUOTE (Oersted @ Dec 10 2008, 11:03 PM) *
2 years delay = 2 MSL´s?


No. Just no.



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