Oppy Vs Spirit Power Consumption Options

[maycm]

From the following "Space" article LINK

Spirit’s solar arrays currently produce about 650 watt hours while Opportunity’s generate up to 700 watt hours, Laubach said. A minimum of 300 watt hours is required for Spirit to function, though Opportunity can operate on slightly less, she added.

What is the reason for the lower power requirements of Oppy?

I thought the two rovers were identical.

[RNeuhaus]

From the following "Space" article LINK
What is the reason for the lower power requirements of Oppy?

I thought the two rovers were identical.

Maybe that Gusev zone requires more energy than Meridiani to advance due to the type of terrain. More slope to down and go up.

Rodolfo

[helvick]

I thought the two rovers were identical.

The only thing I can think of is that Meridiani is a slightly more benign place than Gusev, specifically (as the article indicates) the temperatures are a few degees warmer so the heating requirements in mid winter will be slightly better.

[ElkGroveDan]

From the following "Space" article What is the reason for the lower power requirements of Oppy?

I think it's because Oppy had that stuck heater switch and they shut the heater off. Spirit probably still has the intermittent heating going on.

Just a guess, going from memory.

[imran]

From the following "Space" article LINK
What is the reason for the lower power requirements of Oppy?

I thought the two rovers were identical.

Wasn't Spirit generating close to 900 watt-hours a month or so back?

[helvick]

Wasn't Spirit generating close to 900 watt-hours a month or so back?

Yes but that was in August\September. 956 on Aug 21, 885 on 12 September. The fall of in Insolation is quite rapid at the moment as summer ends, it would have dropped by about 75 watts just because of that. There probably has been some dust build up which would account for some of the additional loss but the largest component is caused by the fact that spirit is travelling down a fairly steep north facing slope while the Noon sun is still in the Southern Sky.

[TheChemist]

spirit is travelling down a fairly steep north facing slope while the Noon sun is still in the Southern Sky.

Spirit was facing north while climbing up Husband Hill. It can't be facing north again going down on the opposite side

[helvick]

Spirit was facing north while climbing up Husband Hill. It can't be facing north again going down on the opposite side 

Good point. I'm not sure of the orientation to be honest but I recall that SS did say they needed to get off slope quickly while the power situation was favourable. I took that to mean that the downward route was predominantly North facing. Looking at the route map it appears that the orientation is probably generally south easterly, tilted at an average of around ~10%. That shouldn't cause too much of a drop in power on it's own.

I'm still convinced that orientation is the main problem, it may be that the missing power is caused by the fact that she's in a valley now and the effective sunset is a lot earlier that it was when she was on top of the hill.

Can anyone estimate what her orientation and average tilt has been over the past week or so?

[maycm]

Spirit was facing north while climbing up Husband Hill. It can't be facing north again going down on the opposite side 

That would only affect it's ability to generate the required amount of power, but the article suggests that it is the power requirement that is different.

Likewise, stuck power heaters etc affect power requirements, but the team have the ability to switch off the heater on Spirit in the same way as they did on Oppy if power becomes tight, so those should equal each other out too.

[Marcel]

The only thing I can think of is that Meridiani is a slightly more benign place than Gusev, specifically (as the article indicates) the temperatures are a few degees warmer so the heating requirements in mid winter will be slightly better.

That must be the main reason. The only other could be slight differences in elektronic efficiency....we have seen other differences (i remember threads before where we found out they aren't exactly identical twins.....). Slight differences in capacitors, coils, semi-conductors, intrinsic dielectrical properties of wiring, length of wiring, heat losses, etc. can add up to some % difference.

[mars loon]

12/5/2005

Significant New Power Information from JPL is here:

PIA03607: Solar Power on Mars

http://photojournal.jpl.nasa.gov/catalog/PIA03607

Original Caption Released with Image:

This chart illustrates the variation in available solar power for each of NASA's twin Mars Exploration Rovers over the course of approximately two Mars years. Two factors affect the amount of available power: the tilt of Mars' axis and the eccentricity of the Mars' orbit about the sun.

The horizontal scale is the number of Martian days (sols) after the Jan. 4, 2004, (Universal Time) landing of Spirit at Mars' Gusev Crater. The vertical scale on the right indicates the amount of available solar power as a ratio of the amount available at the equator when Mars is closest to the sun (perihelion). The red line indicates power availability at Spirit's landing site (Gusev). The blue line indicates power availability at Opportunity's landing site (Meridiani).

The vertical scale on the right applies to the dotted line, indicating the latitude north or south of Mars' equator where the noon sun is overhead at different times of the Martian year.


and more here

PIA03608: Solar-Panel Dust Accumulation and Cleanings

http://photojournal.jpl.nasa.gov/catalog/PIA03608

Original Caption Released with Image:

Air-fall dust accumulates on the solar panels of NASA's Mars Exploration Rovers, reducing the amount of sunlight reaching the solar arrays. Pre-launch models predicted steady dust accumulation. However, the rovers have been blessed with occasional wind events that clear significant amounts of dust from the solar panels.

This graph shows the effects of those panel-cleaning events on the amount of electricity generated by Spirit's solar panels. The horizontal scale is the number of Martian days (sols) after Spirit's Jan. 4, 2005, (Universal Time) landing on Mars. The vertical scale indicates output from the rover's solar panels as a fraction of the amount produced when the clean panels first opened. Note that the gradual declines are interrupted by occasional sharp increases, such as a dust-cleaning event on sol 420.

[RNeuhaus]

Interesting graph. The worst time would be around the Sol 910, it is more than 7 months from now, it is around Junio-Julio.

Rodolfo

[mars loon]

Interesting graph. The worst time would be around the Sol 910, it is more than 7 months from now, it is around Junio-Julio.

Rodolfo

Thats around the next martian winter.

Space Daily has reprinted the chart and captions here:

http://www.spacedaily.com/news/mars-mers-05zzzzzj.html

[ljk4-1]

Rovers Exceed Expectations

http://www.cornellsun.com/news/2006/01/20/...ml&mkey=2150912

[sattrackpro]

There are many differences, but primary is the latitude location difference - secondary differences of considerable significance has been the increase power usage caused by Spirit's balky wheel, (drawing much more current, now remedied by alternate driving, but still a slight factor) and the stark differences in terrain, taking some degree more power to move 1000 meters uphill than it takes to drive 1000 meters on semi-level terrain. Drain on the MER-B batteries have probably been less deep and less frequent than for MER-A overall.

I would think too, having experienced years of working with batteries, that to some degree frequency of movement (driving frequently, versus staying in one local for extended periods of time) effects battery condition and the amount of energy that can be stored with a given potential. MER-A has driven over rougher terrain, causing this deeper and more frequent drain than that of MER-B, hence MER-A batteries would probably require more power supplied longer to reach the same potential that MER-B could achieve with less power supplied, simply due to differences in the condition of the batteries. (MER-B has been frequently parked (virtually) in several places over much of its time on Mars - while MER-A as been more frequently on the move in higher power consumption territory.)

Hence, it would not be unreasonable to expect that the condition of the MER-B battery would be in better overall condition than that of MER-A, and that the MER-A battery would be more difficult to charge to as high a potential as the MER-B battery. One thought to keep in mind - these batteries (like any other) are approaching the point where they will simply refuse to take a full charge, no matter how clean the panels are, or how much sun is available. They are the best that could be built, but all rechargeable batteries have a limit to the number of times they can be charged to the full potential they could achieve when new.