What is the minimum launch vehicle size to reach outer space without a payload?

Northrup Grumman has the aircraft launched Pegasus system. That will put a 450kg load into orbit.

Here’s the Pegasus data sheet.

Here’s the User Guide

@LuckyGuy not exactly tiny…

The current record for smallest earth-based low orbit launch vehicle is held by the Japanese Aerospace Exploration Agency (JAXA), since it’s successful mission on Feb. 3, 2018:

“The Orbital SS-520 is a three-stage, all-solid-fueled launch vehicle standing 9.54 meters tall and 52 centimeters in diameter, weighing in at only 2,600 Kilograms – smaller and lighter than any previous ground-based orbital launch vehicle. As a souped-up Sounding Rocket, SS-520–5 was looking at a rapid launch sequence, planning to reach orbit in under four and a half minutes with only 82 seconds of actual powered flight – creating one of the fastest orbital space launches ever attempted.”

Full mission details & rocket specs here:
https://spaceflight101.com/japan-ss-520-5-launch-success/

@Ltryptophan It’s not tiny but it does something. It puts 1000 pounds into orbit and it does it in a relatively small package.

About a decade ago, RIT, Rochester institute of Technology, had a program called METEOR that used a weather balloon to lift a 4 stage rocket designed to place a cube sat into orbit.
I do not have other info about it.

I started thinking about this another way.
What’s the smallest thing we can send into outer space? I will start with a photon. If I aim my flashlight into the night sky I am sending a stream of photons to the Moon, or Mars or Andromeda or ? and they are traveling at light speed.

Ok, that is not a good answer. Let’s consider sending something. How about a BB? In order to get it into orbit, as a minimum, it must reach orbital velocity. Ignoring friction (which is huge) we can calculate the kinetic energy needed to reach orbit. ½ m v^2. Now we need to figure the mass of fuel and the containers needed to do that. Now we need to figure the kinetic energy that fuel has and calculate the fuel needed to achieve that. And so on.
The Pegasus is a pretty good answer.

Maybe an exotic rail gun will be used in the future to ballistically launch objects. I won’t hold my breath.

SpinLaunch will fling your stuff into space. It won’t be at orbital velocity, so you will need a rocket anyway. https://www.spinlaunch.com/

@RocketGuy That looks like something from a 1930s sci-fi movie.
I didn’t see any info about launch velocity or RPM, but a quick guess at centripetal/centrifugal load indicates a heck of a lot of side load on anything placed inside that sabot. Yikes.
Unless firing solid slugs at something hundreds of miles away, I’d be concerned about my payload turning into a poorly formed pancake.

@RocketGuy I found something on wiki describing the proposed set up. 100 meters in diameter, launch velocity or 8000 km/hr. Using v^{2/r for centripetal acceleration, I calculate ~98,745.68 m/s}2 or 10,000 g ! At release the centripetal acceleration will instantly drop to zero. Quite a shock! Yikes, indeed!

I also wonder how they handle the counterbalance load on their centrifuge after launch.
Did they think this out? It’s hard/difficult to violate the laws of physics.

Maybe they can use their system to produce enriched uranium.

@LuckyGuy… SpinCannon.

They can probably spin water, materials, and fuel to 10,000g without smooshing them flat. To resist a payload at 10,000g, the spinner arm would have to be huge so the unbalance when they release the payload will not be a big percentage. I’ll bet the ground will emanate a big thud, though. I stood next to a Tinius-Olsen pulling a 30,000 lb tensile test before. The floor shook when it broke.

@RocketGuy I couldn’t help myself. I had to do some calcs.

They said they launched a payload “10s of thousand of feet” into the air. I started with 20,000. From that I did a first order calc to get a total flight time of 70 seconds and an initial velocity of 1131 ft/s 344m/s. That means the arm was spinning at 1365 rpm. Since it is an electric motor most likely it was running at 1800 rpm.
I agree that they cold fling water. But a rocket with fuel, electronics, satellite payload sensors, not very likely. You mentioned the ground shaking when the Tinius-Olsen broke the device under test. That ground shaking “whump” would be for a 3 pound load. Imagine what it would be like for a payload 100 times that!

It’s a fun thought if you forget about physics.

@LuckyGuy I’ve see documentatary/promotion video of the spin launch system.
You have correctly identified one of the trickiest problems: how to deal with the sudden shift in balance at the moment of releasing payload. Without compensation the system would tear itself apart quickly.
There is a super-fast mechanism that moves center of the spin axis at the same moment the load is released.

@dabbler Thanks. That mechanism must be very fast and powerful. It will only protect the arm and spin mechanism.
It does not protect against the rapid loss of sideloading on the payload.