Winston Science Fiction was a series, thirty-five, of juveniles published between 1952 and 1961. There was one collection and one non-fiction among them. SF writers mostly, but some more known for other genres. As here(this one and another couple were originally published as by Richard Marsden). All were especially written for the series and distinguished by that rocket on the spine. I frequently looked for that rocket when I was very young. Don’t know that I read all of them back then. Likely not.
Owen and Chuck Spencer should have been suspicious of Dirk Masterson from the start. Owen was the guide for the Time Slip back to the Jurassic era and Chuck was being allowed to go along. Masterson was unco-operative from go, not wanting to prove his identity.
Things only got worse when they went back. Masterson jumps into a jeep and
takes off at high speed, crashing into and shoring out the force field that kept the dinosaurs away from them. And the recall wasn’t for a week.
When Masterson and his partner pulled hunting rifles from their truck, The Spencer brothers knew trouble was here. You see, this was a photography only mission. Killing was illegal.
And finally, Chuck discovers mining equipment and dynamite stored in Masterson’s truck.
A nice little juvenile science fiction novel. I did have problems with one plot line, but won’t give that away. Try it and see what you think. They are available as ebooks.
Not The Baseball Pitcher 
I loved this series when I was a kid. Haven’t read this one, though.
I read and reviewed DANGER, DINOSAURS about a year ago. It has a time-travel twist that I was surprised by. LIke Bill, I was a big fan of the Winston SF series when I was a kid. I really liked Ben Bova’s THE STAR CONQUERERS.
I remember that rocket, although I only saw very few of these as a kid.
It has long been a dream of mine to own the entire series, but I have never come across a single one in VG or better condition (I’d want them all to be in ice-read with perfect DJ, of course, after all, it’s a dream…). I one walked into a used book shop and they had the entire Tom Swift Jr. set in top condition. I just missed getting it. If I ever saw a complete set of these, oh my.
I’ve read this one, long ago, and remember liking it.
Oh, and tell that guy in the picture to leave his girlfriend’s kitty cat alone.