Fastest Spacecraft Ever?!?, Which one is it? Options

[Toma B]

There was statement that recently launched New Horizons is the fastest spacecraft to leave Earth. The velocity was 16.2 km/s relative to the Earth according to "Jonathan's Space Report".

After the Star 48B burn, the payload had reached escape velocity not only with respect to the Earth but also relative to the Sun (The velocity was 16.2 km/s relative to the Earth and I estimate an asymptotic velocity of 12.3 km/s, corresponding to 42.6 km/s relative to the Sun...

So:
New Horizons is fastest to leave Earth at 16.2 km/s (relative to Earth).
Voyager-1 is fastest to leave Solar System at 17.374 km/s (relative to Sun).

Now that is OK. but what is this?
Today's "Astronomy Picture of the Day" features launch of New Horizons and in text bellow image is one particularly interesting link to "Guinness world of records"...
Guinness world of records;
There "Mr. Guinness" claims that the fastest spacecrafts ever, were two Solar probes "Helios 1&2"...According to him those spacecrafts had speed of 252,800 km/h which is staggering 70.2 km/s...BUT RELATIVE TO WHAT?????
Can somebody explain this?

[ljk4-1]

Via Solar Array to the Outer Planets

New Scientist is covering the work of Rudolph Meyer (UCLA), who envisions a vehicle that sounds for all the world like a cross between a solar sail and an ion engine. And in a way, it is: Imagine a flexible solar panel a solid 3125 square meters in size, and imagine this ’solar-electric membrane’ weighing no more than 16 grams per square meter, far lighter than today’s technology allows. I’ll be anxious to see the paper when it’s published in Acta Astronautica, but the gist of the design seems to be this: the solar membrane would power an ion engine array which, conventionally enough, draws xenon ions through a powerful electric grid to create thrust.

The membrane, stabilized by additional ion engines at the corners, could reach remarkable speeds. Meyer talks about 666,000 kilometers per hour — that’s one year to Pluto, and an obvious invitation out into the Kuiper Belt. No show stoppers here, but clearly a design heavily dependent on advances in thin film arrays. I always listen to Geoffrey Landis (NASA GRC) about such matters; he is, after all, the man Robert Forward declared to be his successor in interstellar studies. And Landis is quoted as saying of Rudolph’s idea, “…the extremely high-energy ion-propulsion vehicles he proposes may be a practical alternative technology for future missions to the edge of interstellar space.”

Full article here:

http://www.centauri-dreams.org/?p=638

[djellison]

Meyer talks about 666,000 kilometers per hour — that's one year to Pluto,."

Yes - but how long to accelerate to 666000 kph ?

Doug

[ljk4-1]

Yes - but how long to accelerate to 666000 kph ?

Doug

I don't know. If anyone can find the paper or even just more
information on the plan, please post it here, thanks!