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Comment by raldi | Hacker News Reader

> Payloads replacing Balance mass should perform some type of scientific or technological function adding to our knowledge base while closely matching the volume and weight characteristics of the original Balance mass.

Um, the one being replaced was solid tungsten, which is almost twice as dense as lead. How is anything going to come close to matching that?

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> Because of the high density of tungsten, it is unlikely that payload concepts may be proposed that identically match the characteristics of the MSL BMDs. To maximize the potential for innovative concepts while still achieving the desired spacecraft EDL performance, NASA is requesting that proposed concepts target 90% of the original MSL BMD mass while matching the volumetric dimensions used for MSL.

Still, I agree with you. It's a very difficult target.

Where is that quote from?

It seems to me that the only way to hit the 90% target would be to include 270kg of dead-weight tungsten, and fit all the science into a 30kg budget.

Logging into innocentive lets you see more details about each challenge.

EDIT: To your second point: Even though it's 300 kg total, it looks like that's allocated to 2 75 kg objects and 6 25 kg objects. I would assume that means much less weight/space per unit to work with, given the dead weight to go along with it.

The relevant constraint isn't mass, but volume. Essentially you're limited you to a cube 12 cm on a side (plus 1 cm³ for every 19.25 g of payload mass).

What are you basing that claim on? The quotes elsewhere in this thread seem to contradict what you're saying.

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